I have a pretty simple script that is something like the following:
#!/bin/bash
VAR1="$1"
MOREF='sudo run command against $VAR1 | grep name | cut -c7-'
echo $MOREF
When I run this script from the command line and pass it the arguments, I am not getting any output. However, when I run the commands contained within the $MOREF variable, I am able to get output.
How can one take the results of a command that needs to be run within a script, save it to a variable, and then output that variable on the screen?
In addition to backticks `command`, command substitution can be done with $(command) or "$(command)", which I find easier to read, and allows for nesting.
OUTPUT=$(ls -1)
echo "${OUTPUT}"
MULTILINE=$(ls \
-1)
echo "${MULTILINE}"
Quoting (") does matter to preserve multi-line variable values; it is optional on the right-hand side of an assignment, as word splitting is not performed, so OUTPUT=$(ls -1) would work fine.
$(sudo run command)
If you're going to use an apostrophe, you need `, not '. This character is called "backticks" (or "grave accent"):
#!/bin/bash
VAR1="$1"
VAR2="$2"
MOREF=`sudo run command against "$VAR1" | grep name | cut -c7-`
echo "$MOREF"
Some Bash tricks I use to set variables from commands
Sorry, there is a loong answer, but as bash is a shell, where the main goal is to run other unix commands and react on result code and/or output, ( commands are often piped filter, etc... ).
Storing command output in variables is something basic and fundamental.
Therefore, depending on
compatibility (posix)
kind of output (filter(s))
number of variable to set (split or interpret)
execution time (monitoring)
error trapping
repeatability of request (see long running background process, further)
interactivity (considering user input while reading from another input file descriptor)
do I miss something?
First simple, old (obsolete), and compatible way
myPi=`echo '4*a(1)' | bc -l`
echo $myPi
3.14159265358979323844
Compatible, second way
As nesting could become heavy, parenthesis was implemented for this
myPi=$(bc -l <<<'4*a(1)')
Using backticks in script is to be avoided today.
Nested sample:
SysStarted=$(date -d "$(ps ho lstart 1)" +%s)
echo $SysStarted
1480656334
bash features
Reading more than one variable (with Bashisms)
df -k /
Filesystem 1K-blocks Used Available Use% Mounted on
/dev/dm-0 999320 529020 401488 57% /
If I just want a used value:
array=($(df -k /))
you could see an array variable:
declare -p array
declare -a array='([0]="Filesystem" [1]="1K-blocks" [2]="Used" [3]="Available" [
4]="Use%" [5]="Mounted" [6]="on" [7]="/dev/dm-0" [8]="999320" [9]="529020" [10]=
"401488" [11]="57%" [12]="/")'
Then:
echo ${array[9]}
529020
But I often use this:
{ read -r _;read -r filesystem size using avail prct mountpoint ; } < <(df -k /)
echo $using
529020
( The first read _ will just drop header line. ) Here, in only one command, you will populate 6 different variables (shown by alphabetical order):
declare -p avail filesystem mountpoint prct size using
declare -- avail="401488"
declare -- filesystem="/dev/dm-0"
declare -- mountpoint="/"
declare -- prct="57%"
declare -- size="999320"
declare -- using="529020"
Or
{ read -a head;varnames=(${head[#]//[K1% -]});varnames=(${head[#]//[K1% -]});
read ${varnames[#],,} ; } < <(LANG=C df -k /)
Then:
declare -p varnames ${varnames[#],,}
declare -a varnames=([0]="Filesystem" [1]="blocks" [2]="Used" [3]="Available" [4]="Use" [5]="Mounted" [6]="on")
declare -- filesystem="/dev/dm-0"
declare -- blocks="999320"
declare -- used="529020"
declare -- available="401488"
declare -- use="57%"
declare -- mounted="/"
declare -- on=""
Or even:
{ read _ ; read filesystem dsk[{6,2,9}] prct mountpoint ; } < <(df -k /)
declare -p mountpoint dsk
declare -- mountpoint="/"
declare -a dsk=([2]="529020" [6]="999320" [9]="401488")
(Note Used and Blocks is switched there: read ... dsk[6] dsk[2] dsk[9] ...)
... will work with associative arrays too: read _ disk[total] disk[used] ...
Other related sample: Parsing xrandr output: and end of Firefox tab by bash in a size of x% of display size? or at AskUbuntu.com Parsing xrandr output
Dedicated fd using unnamed fifo:
There is an elegent way! In this sample, I will read /etc/passwd file:
users=()
while IFS=: read -u $list user pass uid gid name home bin ;do
((uid>=500)) &&
printf -v users[uid] "%11d %7d %-20s %s\n" $uid $gid $user $home
done {list}</etc/passwd
Using this way (... read -u $list; ... {list}<inputfile) leave STDIN free for other purposes, like user interaction.
Then
echo -n "${users[#]}"
1000 1000 user /home/user
...
65534 65534 nobody /nonexistent
and
echo ${!users[#]}
1000 ... 65534
echo -n "${users[1000]}"
1000 1000 user /home/user
This could be used with static files or even /dev/tcp/xx.xx.xx.xx/yyy with x for ip address or hostname and y for port number or with the output of a command:
{
read -u $list -a head # read header in array `head`
varnames=(${head[#]//[K1% -]}) # drop illegal chars for variable names
while read -u $list ${varnames[#],,} ;do
((pct=available*100/(available+used),pct<10)) &&
printf "WARN: FS: %-20s on %-14s %3d <10 (Total: %11u, Use: %7s)\n" \
"${filesystem#*/mapper/}" "$mounted" $pct $blocks "$use"
done
} {list}< <(LANG=C df -k)
And of course with inline documents:
while IFS=\; read -u $list -a myvar ;do
echo ${myvar[2]}
done {list}<<"eof"
foo;bar;baz
alice;bob;charlie
$cherry;$strawberry;$memberberries
eof
Practical sample parsing CSV files:
As this answer is loong enough, for this paragraph,
I just will let you refer to
this answer to How to parse a CSV file in Bash?, I read a file by using an unnamed fifo, using syntax like:
exec {FD}<"$file" # open unnamed fifo for read
IFS=';' read -ru $FD -a headline
while IFS=';' read -ru $FD -a row ;do ...
... But using bash loadable CSV module.
On my website, you may find the same script, reading CSV as inline document.
Sample function for populating some variables:
#!/bin/bash
declare free=0 total=0 used=0 mpnt='??'
getDiskStat() {
{
read _
read _ total used free _ mpnt
} < <(
df -k ${1:-/}
)
}
getDiskStat $1
echo "$mpnt: Tot:$total, used: $used, free: $free."
Nota: declare line is not required, just for readability.
About sudo cmd | grep ... | cut ...
shell=$(cat /etc/passwd | grep $USER | cut -d : -f 7)
echo $shell
/bin/bash
(Please avoid useless cat! So this is just one fork less:
shell=$(grep $USER </etc/passwd | cut -d : -f 7)
All pipes (|) implies forks. Where another process have to be run, accessing disk, libraries calls and so on.
So using sed for sample, will limit subprocess to only one fork:
shell=$(sed </etc/passwd "s/^$USER:.*://p;d")
echo $shell
And with Bashisms:
But for many actions, mostly on small files, Bash could do the job itself:
while IFS=: read -a line ; do
[ "$line" = "$USER" ] && shell=${line[6]}
done </etc/passwd
echo $shell
/bin/bash
or
while IFS=: read loginname encpass uid gid fullname home shell;do
[ "$loginname" = "$USER" ] && break
done </etc/passwd
echo $shell $loginname ...
Going further about variable splitting...
Have a look at my answer to How do I split a string on a delimiter in Bash?
Alternative: reducing forks by using backgrounded long-running tasks
In order to prevent multiple forks like
myPi=$(bc -l <<<'4*a(1)'
myRay=12
myCirc=$(bc -l <<<" 2 * $myPi * $myRay ")
or
myStarted=$(date -d "$(ps ho lstart 1)" +%s)
mySessStart=$(date -d "$(ps ho lstart $$)" +%s)
This work fine, but running many forks is heavy and slow.
And commands like date and bc could make many operations, line by line!!
See:
bc -l <<<$'3*4\n5*6'
12
30
date -f - +%s < <(ps ho lstart 1 $$)
1516030449
1517853288
So we could use a long running background process to make many jobs, without having to initiate a new fork for each request.
You could have a look how reducing forks make Mandelbrot bash, improve from more than eight hours to less than 5 seconds.
Under bash, there is a built-in function: coproc:
coproc bc -l
echo 4*3 >&${COPROC[1]}
read -u $COPROC answer
echo $answer
12
echo >&${COPROC[1]} 'pi=4*a(1)'
ray=42.0
printf >&${COPROC[1]} '2*pi*%s\n' $ray
read -u $COPROC answer
echo $answer
263.89378290154263202896
printf >&${COPROC[1]} 'pi*%s^2\n' $ray
read -u $COPROC answer
echo $answer
5541.76944093239527260816
As bc is ready, running in background and I/O are ready too, there is no delay, nothing to load, open, close, before or after operation. Only the operation himself! This become a lot quicker than having to fork to bc for each operation!
Border effect: While bc stay running, they will hold all registers, so some variables or functions could be defined at initialisation step, as first write to ${COPROC[1]}, just after starting the task (via coproc).
Into a function newConnector
You may found my newConnector function on GitHub.Com or on my own site (Note on GitHub: there are two files on my site. Function and demo are bundled into one unique file which could be sourced for use or just run for demo.)
Sample:
source shell_connector.sh
tty
/dev/pts/20
ps --tty pts/20 fw
PID TTY STAT TIME COMMAND
29019 pts/20 Ss 0:00 bash
30745 pts/20 R+ 0:00 \_ ps --tty pts/20 fw
newConnector /usr/bin/bc "-l" '3*4' 12
ps --tty pts/20 fw
PID TTY STAT TIME COMMAND
29019 pts/20 Ss 0:00 bash
30944 pts/20 S 0:00 \_ /usr/bin/bc -l
30952 pts/20 R+ 0:00 \_ ps --tty pts/20 fw
declare -p PI
bash: declare: PI: not found
myBc '4*a(1)' PI
declare -p PI
declare -- PI="3.14159265358979323844"
The function myBc lets you use the background task with simple syntax.
Then for date:
newConnector /bin/date '-f - +%s' #0 0
myDate '2000-01-01'
946681200
myDate "$(ps ho lstart 1)" boottime
myDate now now
read utm idl </proc/uptime
myBc "$now-$boottime" uptime
printf "%s\n" ${utm%%.*} $uptime
42134906
42134906
ps --tty pts/20 fw
PID TTY STAT TIME COMMAND
29019 pts/20 Ss 0:00 bash
30944 pts/20 S 0:00 \_ /usr/bin/bc -l
32615 pts/20 S 0:00 \_ /bin/date -f - +%s
3162 pts/20 R+ 0:00 \_ ps --tty pts/20 fw
From there, if you want to end one of background processes, you just have to close its fd:
eval "exec $DATEOUT>&-"
eval "exec $DATEIN>&-"
ps --tty pts/20 fw
PID TTY STAT TIME COMMAND
4936 pts/20 Ss 0:00 bash
5256 pts/20 S 0:00 \_ /usr/bin/bc -l
6358 pts/20 R+ 0:00 \_ ps --tty pts/20 fw
which is not needed, because all fd close when the main process finishes.
As they have already indicated to you, you should use `backticks`.
The alternative proposed $(command) works as well, and it also easier to read, but note that it is valid only with Bash or KornShell (and shells derived from those),
so if your scripts have to be really portable on various Unix systems, you should prefer the old backticks notation.
I know three ways to do it:
Functions are suitable for such tasks:**
func (){
ls -l
}
Invoke it by saying func.
Also another suitable solution could be eval:
var="ls -l"
eval $var
The third one is using variables directly:
var=$(ls -l)
OR
var=`ls -l`
You can get the output of the third solution in a good way:
echo "$var"
And also in a nasty way:
echo $var
Just to be different:
MOREF=$(sudo run command against $VAR1 | grep name | cut -c7-)
When setting a variable make sure you have no spaces before and/or after the = sign. I literally spent an hour trying to figure this out, trying all kinds of solutions! This is not cool.
Correct:
WTFF=`echo "stuff"`
echo "Example: $WTFF"
Will Fail with error "stuff: not found" or similar
WTFF= `echo "stuff"`
echo "Example: $WTFF"
If you want to do it with multiline/multiple command/s then you can do this:
output=$( bash <<EOF
# Multiline/multiple command/s
EOF
)
Or:
output=$(
# Multiline/multiple command/s
)
Example:
#!/bin/bash
output="$( bash <<EOF
echo first
echo second
echo third
EOF
)"
echo "$output"
Output:
first
second
third
Using heredoc, you can simplify things pretty easily by breaking down your long single line code into a multiline one. Another example:
output="$( ssh -p $port $user#$domain <<EOF
# Breakdown your long ssh command into multiline here.
EOF
)"
You need to use either
$(command-here)
or
`command-here`
Example
#!/bin/bash
VAR1="$1"
VAR2="$2"
MOREF="$(sudo run command against "$VAR1" | grep name | cut -c7-)"
echo "$MOREF"
If the command that you are trying to execute fails, it would write the output onto the error stream and would then be printed out to the console.
To avoid it, you must redirect the error stream:
result=$(ls -l something_that_does_not_exist 2>&1)
This is another way and is good to use with some text editors that are unable to correctly highlight every intricate code you create:
read -r -d '' str < <(cat somefile.txt)
echo "${#str}"
echo "$str"
You can use backticks (also known as accent graves) or $().
Like:
OUTPUT=$(x+2);
OUTPUT=`x+2`;
Both have the same effect. But OUTPUT=$(x+2) is more readable and the latest one.
Here are two more ways:
Please keep in mind that space is very important in Bash. So, if you want your command to run, use as is without introducing any more spaces.
The following assigns harshil to L and then prints it
L=$"harshil"
echo "$L"
The following assigns the output of the command tr to L2. tr is being operated on another variable, L1.
L2=$(echo "$L1" | tr [:upper:] [:lower:])
Mac/OSX nowadays come with old Bash versions, ie GNU bash, version 3.2.57(1)-release (arm64-apple-darwin21). In this case, one can use:
new_variable="$(some_command)"
A concrete example:
newvar="$(echo $var | tr -d '123')"
Note the (), instead of the usual {} in Bash 4.
Some may find this useful.
Integer values in variable substitution, where the trick is using $(()) double brackets:
N=3
M=3
COUNT=$N-1
ARR[0]=3
ARR[1]=2
ARR[2]=4
ARR[3]=1
while (( COUNT < ${#ARR[#]} ))
do
ARR[$COUNT]=$((ARR[COUNT]*M))
(( COUNT=$COUNT+$N ))
done
I have the shell script:
#!/bin/bash
export LD=$(lsb_release -sd | sed 's/"//g')
export ARCH=$(uname -m)
export VER=$(lsb_release -sr)
# Load the test function
/bin/bash -c "lib/test.sh"
echo $VER
DISTROS=('Arch'
'CentOS'
'Debian'
'Fedora'
'Gentoo')
for I in "${DISTROS[#]}"
do
i=$(echo $I | tr '[:upper:]' '[:lower:]') # convert distro string to lowercase
if [[ $LD == "$I"* ]]; then
./$ARCH/${i}.sh
fi
done
As you can see it should run a shell script, depending on which architecture and OS it is run on. It should first run the script lib/test.sh before it runs this architecture and OS-specific script. This is lib/test.sh:
#!/bin/bash
function comex {
which $1 >/dev/null 2>&1
}
and when I run it on x86_64 Arch Linux with this x86_64/arch.sh script:
#!/bin/bash
if comex atom; then
printf "Atom is already installed!"
elif comex git; then
printf "Git is installed!"
fi
it returned the output:
rolling
./x86_64/arch.sh: line 3: comex: command not found
./x86_64/arch.sh: line 5: comex: command not found
so clearly the comex shell function is not correctly loaded by the time the x86_64/arch.sh script is run. Hence I am confused and wondering what I need to do in order to correctly define the comex function such that it is correctly loaded in this architecture- and OS-dependent final script.
I have already tried using . "lib/test.sh" instead of /bin/bash -c "lib/test.sh" and I received the exact same error. I have also tried adding . "lib/test.sh" to the loop, just before the ./$ARCH/${i}.sh line. This too failed, returning the same error.
Brief answer: you need to import your functions using . or source instead of bash -c:
# Load the test function
source "lib/test.sh"
Longer answer: when you call script with bash -c, a child process is created. This child process sees all exported variables (including functions) from parent process. But not vice versa. So, your script will never see comex function. Instead you need to include script code directly in current script and you do so by using . or source commands.
Part 2. After you "sourced" lib/test.sh, your main script is able to use comex function. But arch scripts won't see this function because it is not exported to them. Your need to export -f comex:
#!/bin/bash
function comex {
which $1 >/dev/null 2>&1
}
export -f comex
I'm building a shell script that will run nightly with the help of crontab and my script keeps bombing out and giving me the error "Syntax error: word unexpected (expected "do").
The script itself is creating a new directory for each MySQL file it finds in a directory and then copies the files to a created directory from the respective mysqldump directory. Please let me know if I am on the right track with this code and what could be causing my end of file error. I am new to shell scripting and would accept any advice given. If there is a better way to write my code then feel free to help in that respect as well.
CDPATH="/backups/mysql"
#
now=$(date +"%Y_%m_%d")
#
# Find Directory Name
#
for file in */; do
dir=${file%/}
if [[ -e "$dir"]]
then
echo "Directory Exists!"
else
echo "Directory doesn't exist."
fi
done
#
# Copy MySQL Databases
#
while [ -d $dir ]; do # Check existing Dirs
cp -upf /dbase/files/*.sql /backups/mysql/$dir/$now # If Dir exists, create copy
if [ ! -d $dir ]; then # If Dir nonexistant create
mkdir -p $dir
cp -upf /dbase/files/*.sql /backups/mysql/$dir/$now
else # If all else fails just create a copy in /mysql
cp -upf /dbase/files/*.sql /backups/mysql/$dir/$now
fi
done
Thanks for the help in advance!
1. do not use "then" after "else"
2. The second line may does not what you want. It just set the variable dir to the string "dir (/backups/mysql/*)"
... obsolete since question has changed.
I assume, files in the following form ...
/dbase/files/db1.sql
/dbase/files/db2.sql
...
... should be backed up to the following destination:
/backups/mysql/db1/2014_11_18/db1.sql
#!/bin/bash
BACKUP_DIR="/backups/mysql/"
FILE_DIR=/dbase/files/
now=$(date +"%Y_%m_%d")
# setting the input field seperator to newline
IFS=$'\n'
# find db backups and loop over
for file in $(find ${FILE_DIR} -maxdepth 1 -name "*.sql" -type f -exec basename {} \;); do
# create backup directory:
mkdir -p "${BACKUP_DIR}${file%.sql}/${now}"
# copy file over
cp "${FILE_DIR}${file}" "${BACKUP_DIR}${file%.sql}/${now}/"
done
Convert the script to unix encoding:
dos2unix script.sh
Annotate gets you as far as seeing the most recent change to that line, if that change is a merge then I have no choice but to trawl through the revision history and find the next time it was modified.
I've also tried hg grep -l '[contents of line]' but:
a) I can't figure out how to target specific files (so it takes forever in a moderately sized repo)
b) It seems to only return the last revision number
The following link is vaguely similar -
How to find all changsets where a reference to a function was modified?
Use Tortoisehg:
View -> Manifest
Right click on file interested in and click "File History"
click "annotate with revision numbers"
The top panel allows you to quickly see the history of the file in terms of commits, the bottom panel shows the annotated file based upon the selected version in the top panel.
Using the response of arielf without an extra script:
UNIX:
command:
hg log --template '{rev}\n' <FILE> |
xargs -I # hg grep <PATTERN> -r # <FILE>
you can use this to add an alias to your configuration file (.hgrc):
[alias]
_grep_line_in_history = ! $HG log --template '{rev}\n' $2 |
xargs -I # hg grep '$1' -r # $2
WINDOWS:
command:
FOR /F "usebackq" %i IN (`hg log --template "{rev}\n" <FILE>`) DO
#(echo %i & hg grep <PATTERN> -r %i <FILE>)
alias:
[alias]
_grep_line_in_history = ! FOR /F "usebackq" %i IN
(`%HG% log --template "{rev}\n" "$2"`) DO #(echo %i & %HG% grep "$1" -r %i "$2")
I think this requires a bit of (two-step) programming.
The following shell script works pretty well for me. It prints both the revisions and the matching lines. If you only want the revisions list, you may add a step to strip the matching text and leave only the revision prefix, and possibly pipe through 'sort -u':
#!/bin/bash
#
# script to grep for a pattern in all revisions of a file
# Usage: scriptname 'pattern' filepath
#
function fatal() {
echo "$#" 1>&2
exit 1
}
function usage() {
echo "$#" 1>&2
fatal Usage: $0 pattern file
}
case "$1" in
'') usage 'missing pattern to search for' ;;
*) Pat="$1" ;;
esac
if [ "$2" != '' ]; then
File="$2"
else
usage 'must pass file as 2nd argument'
fi
# -- generate list of revisions (change-sets) involving $File
for rev in `hg log --template '{rev}\n' $File`; do
# -- grep the wanted pattern in that particular revision
hg grep "$Pat" -r $rev $File
done
Notes:
not fully foolproof (e.g. quotes in the pattern)
I don't check for file existence to support renamed/removed files as well
What's the best way to check in script if there're uncommitted changes in mercurial's working tree.
(the way I would with git diff --quiet in git)
In mercurial 1.4 and later you can use the summary command, which gives output like this when changes exist:
$ hg summary
parent: 0:ad218537bdef tip
commited
branch: default
commit: 1 modified
update: (current)
and this post-commit:
$ hg summary
parent: 1:ef93d692f646 tip
sfsdf
branch: default
commit: (clean)
update: (current)
Alternately, you could install the prompt extension and do something like this:
$ hg prompt '{status}'
which will output a ! or ? or nothing as appropriate.
Both of those, of course, are just alternate text outputs. I couldn't find anything that used the exit code directly, but since $? checks the last command in a pipe you could do?
hg summary | grep -q 'commit: (clean)'
which will set $? non-zero if any changes are uncommitted:
$ hg summary | grep -q 'commit: (clean)' ; echo $?
0
$ echo more >> that
$ hg summary | grep -q 'commit: (clean)' ; echo $?
1
You can also run hg id. If the hash ends with a + it indicates the working copy has changes. This should even work with old versions of hg.
It sounds like you're already using zsh; well, a couple days ago I helped to update the Mercurial support for the built-in VCS_INFO for putting VCS info in your prompt. Slated for the next release is support for showing changes to the working directory (among other things). If you don't want to wait you can grab the necessary files from CVS.
At the moment my prompt includes this (using only built-in zsh functionality):
(hg)[1801+ branchname somemq.patch, anycurrentbookmarks]
I use:
hg status -m -a -r -d -u
If no changes with tracked files, then the command output is an empty string.
I use this bash-snippet for some time now:
if [[ $(hg status 2>/dev/null) ]]
then
# do something
fi
Both id and summary are slower than status, so this is the fastest way I currently know, ignoring untracked files:
[[ -z `hg status | grep -v '^?'` ]] && echo no-changes || echo has-changes
There should be something more elegant than simply
[ `hg st |wc -l` -eq 0 ] && echo hi