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+$N ))
done
I run Modelsim in the cmd from a python program.
I use the following code which call a tcl script which run the modelsim:
os.system("vsim -c -do top_tb_simulate_reg.tcl " )
The tcl script contain the following:
vsim -voptargs="+acc" +UVM_TESTNAME=test_name +UVM_MAX_QUIT_COUNT=1 +UVM_VERBOSITY=UVM_LOW \
-t 1ps -L unisims_verm -L generic_baseblocks_v2_1_0 -L axi_infrastructure_v1_1_0 \
-L dds_compiler_v6_0_12 -lib xil_defaultlib xil_defaultlib.girobo2_tb_top \
xil_defaultlib.glbl
I want that the value of the +UVM_TESTNAME will be an argument which I passed from the cmd when I execute:
os.system("vsim -c -do top_tb_simulate_reg.tcl " )
How can I do it?
I tried the following with no succees:
Python script:
os.system("vsim -c -do top_tb_simulate_reg.tcl axi_rd_only_test" )
Simulation file (tcl script)
vsim -voptargs="+acc" +UVM_TESTNAME=$argv +UVM_MAX_QUIT_COUNT=1 +UVM_VERBOSITY=UVM_LOW \
-t 1ps -L unisims_verm -L generic_baseblocks_v2_1_0 -L axi_infrastructure_v1_1_0 \
-L dds_compiler_v6_0_12 -lib xil_defaultlib xil_defaultlib.girobo2_tb_top \
xil_defaultlib.glbl
I got the following error:
# ** Error: (vsim-3170) Could not find 'C:/raft/raftortwo/girobo2/ver/sim/work.axi_rd_only_test'.
The problem is that the vsim binary is doing its own processing of the arguments, and that is interfering. While yes, you can probably find a way around this by reading the vsim documentation, the simplest way around this is to pass values via environment variables. They're inherited by a process from its parent process, and are fine for passing most things. (The exception are security tokens, which should always be passed in files with correctly-set permissions, rather than either environment variables or command-line arguments.)
In your python code:
# Store the value in the *inheritable* environment
os.environ["MY_TEST_CASE"] = "axi_rd_only_test"
# Do the call; the environment gets passed over behind the scenes
os.system("vsim -c -do top_tb_simulate_reg.tcl " )
In your tcl code:
# Read out of the inherited environment
set name $env(MY_TEST_CASE)
# Use it! (Could do this as one line, but that's hard to read)
vsim -voptargs="+acc" +UVM_TESTNAME=$name +UVM_MAX_QUIT_COUNT=1 +UVM_VERBOSITY=UVM_LOW \
-t 1ps -L unisims_verm -L generic_baseblocks_v2_1_0 -L axi_infrastructure_v1_1_0 \
-L dds_compiler_v6_0_12 -lib xil_defaultlib xil_defaultlib.girobo2_tb_top \
xil_defaultlib.glbl
Late to the party but I found a great workaround for your obstacle. The do command within Modelsim's TCL instance does accept parameters. See command reference.
vsim -c -do filename.tcl can't take parameters, but you can use vsim -c -do "do filename.tcl params".
In your case this translates to os.system('vsim -c -do "do top_tb_simulate_reg.tcl axi_rd_only_test"'). Your .tcl script will find the parameter passed through the variable $1.
I hope to helps anyone!
I'm new to tcl. I'm trying to run some commands with tcl script.
I searched online and came to know that we can run unix commands with tcl using exec
I executed the following;
perl -i -p -e 's/hello linux./hello fedora. /g;' sample1.txt
from the commandline and it worked. it replaced all the occurences of hello linux with hello fedora.
I tried executing the same command in my tcl script.
set result [exec perl -i -p -e 's/hello linux./hello fedora. /g;' sample.txt]
I got the below error :
child process exited abnormally
I also tried using sed command. I got the same error. I guess there is something wrong with the syntax. I searched online but i couldn't figure it out on my own.
' is not a grouping character in tcl. The equivalent grouping in tcl is {}. Therefore the correct statement is:
exec perl -i -p -e {s/hello linux./hello fedora. /g;} sample.txt
Or even:
exec perl -i -p -e "s/hello linux./hello fedora. /g;" sample.txt
I'm having an issue passing variables to a Bash script using QSub.
Assume I have a Bash script named example. The format of example is the following:
#!/bin/bash
# (assume other variables have been set)
echo $1 $2 $3 $4
So, executing "bash example.sh this is a test" on Terminal (I am using Ubuntu 12.04.3 LTS, if that helps) produces the output "this is a test".
However, when I enter "qsub -v this,is,a,test example.sh", I get no output. I checked the output file that QSub produces, but the line "this is a test" is nowhere to be found.
Any help would be appreciated.
Thank you.
Using PBSPro or SGE, arguments can simply be placed after the script name as may seem intuitive.
qsub example.sh hello world
In Torque, command line arguments can be submitted using the -F option. Your example.sh will look something like this:
#!/bin/bash
echo "$1 $2"
and your command like so:
qsub -F "hello world" example.sh
Alternatively, environment variables can be set using -v with a comma-separated list of variables.
#!/bin/bash
echo "$FOO $BAR"
and your command like so:
qsub -v FOO="hello",BAR="world" example.sh
(This may be better phrased as a comment on #William Hay's answer, but I don't have the reputation to do so.)
Not sure which batch scheduler you are using but on PBSPro or SGE then submitting with qsub example.sh this is a test should do what you want.
The Torque batch scheduler doesn't (AFAIK) allow passing command line arguments to the script this way. You would need to create a script looking something like this.
#!/bin/bash
echo $FOO
Then submit it with a command like:
qsub -v FOO="This is a test" example.sh
In my TCL script I use rsync command and unfortunately it is refusing to sync path contain "*" character.
Code Example:
set srs "/users/home/username/common/*"
catch {exec rsync -av $src /tmp} res
puts $res
Output:
building file list ... done
sent 29 bytes received 20 bytes 98.00 bytes/sec
total size is 0 speedup is 0.00
rsync: link_stat "/users/home/username/common/*" failed: No such file or directory (2)
rsync error: some files could not be transferred (code 23) at main.c(977) [sender=2.6.9]
while executing
"exec rsync -rLptgov $src /tmp "
The canonical way of writing that is:
set srs "/users/home/username/common/*"
catch {exec rsync -av {*}[glob $src] /tmp} res
puts $res
This is because Tcl doesn't expand glob metacharacters by default; it's safer that way and easier to write correct code (it's hard to write good shell code that is resistant to problems in this area) but it does mean that you need to do a little extra work. The extra work is:
Ask for glob expansion of $srs with the glob command. That returns a list.
Ask for expansion of the list out of the glob by using the {*} pseudo-operator (it's not an operator — it's technically a kind of syntax — but it works a lot like one).
If you're using Tcl 8.4 (or before!) then you do it a bit different way:
set srs "/users/home/username/common/*"
catch {eval [list exec rsync -av] [glob $src] [list /tmp]} res
puts $res
OK, that's sometimes often shortened by leaving out the list bits (and there are many more obscure ways of writing it!) but that's a bad habit as it can cause huge problems when dealing with variables with values that aren't “nice”, e.g., with spaces in pathnames. If you have 8.5 or later, use {*}. Really.
To elaborate on what GrAnd said, you have to build the list of source files explicitly, probably using glob, so you'd do it like this
set cmd [concat [list exec rsync -av] \
[glob -nocomplain /users/home/username/common/*]]
lappend cmd /tmp
catch {eval $cmd} res
puts $res
or, alternatively, use {*} to expand the agument list for exec (this is for Tcl >= 8.5), like this:
set cmd [concat [list rsync -av] \
[glob -nocomplain /users/home/username/common/*]]
lappend cmd /tmp
catch {exec {*}$cmd} res
puts $res
Update: fixed example so that it really works.
That's because tcl interpreter does not expand the '*' symbol as shell does.
For example:
$ tclsh
% cd /usr
% exec ls -d *
ls: *: No such file or directory
% exec sh -c "ls -d *"
X11R6
bin
docs
etc
...