I want to use the following command in a tcl script :
sed -n '452,$ { /wire/ {p;q} }' /tmp/foo
For that I have changed this command as follow :
set MIDLINE2 [ exec sed -n {1134,$ {/wire/{=;q}}} foo.txt ]
It gives me correct answer but in place 1134 I want to use variable $MIDLINE that has value 1134. How can I do that ? Please suggest some way.
This is a simple problem of quoting. You're using curly braces which inhibits variable substitution. Since you want variable substitution you need to use something else.
set MIDLINE2 [ exec sed -n "$MIDLINE,\$ {/wire/{=;q}}" foo.txt ]
Notice that you have to put a backslash in front of the literal $, otherwise Tcl will try to substitute that, too.
Related
I have a Perl script that uses some local variables as per below:
my $cool_variable="Initial value";
COOLVAR="Initial value for COOLVAR"
I would like to replace the content between the quotes using a bash script.
I got it to work for a non-variable like below:
#!/bin/sh
dummy_var="Replaced value"
sed -i -r "s#^(COOLVAR=).*#\1$dummy_var#" perlscript.pl
But if I replace it with cool_variable or $cool_variable:
sed -i -r "s#^($cool_variable=).*#\1$dummy_var#" perlscript.pl
It does not work..
The are multiple code injection bugs in that snippet. You shouldn't be generating code from the shell or sed.
Say you have
var=COOLVAR
val=coolval
As per How can I process options using Perl in -n or -p mode?, you can use any of
perl -spe's{^$var=\K.*}{"\Q$val\E";};' -- -var="$var" -val="$val" perlscript.pl
var=var val=val perl -pe's{^$ENV{var}=\K.*}{"\Q$ENV{val}\E";};' perlscript.pl
export var
export val
perl -pe's{^$ENV{var}=\K.*}{"\Q$ENV{val}\E";};' perlscript.pl
to transform
COOLVAR="dummy";
HOTVAR="dummy";
into
COOLVAR="coolvar";
HOTVAR="dummy";
The values are passed to the program using arguments to avoid injecting them into the fixer, and the fixer uses Perl's quotemeta (aka \Q..\E) to quote special characters.
Note that $var is assumed to be a valid identifier. No validation checks are performed. This program is absolutely unsafe using untrusted input.
Use -i to modify the file in place.
I am new to bash script.
I am getting some json response and i get only one property from the response. I want to save it to a variable but it is not working
token=$result |sed -n -e 's/^.*access_token":"//p' | cut -d'"' -f1
echo $token
it returns blank line.
I cannot use jq or any third party tools.
Please let me know what I am missing.
Your command should be:
token=$(echo "$result" | sed -n -e 's/^.*access_token":"//p' | cut -d'"' -f1)
You need to use echo to print the contents of the variable over standard output, and you need to use a command substitution $( ) to assign the output of the pipeline to token.
Quoting your variables is always encouraged, to avoid problems with white space and glob characters like *.
As an aside, note that you can probably obtain the output using something like:
token=$(jq -r .access_token <<<"$result")
I know you've said that you can't use jq but it's a standalone binary (no need to install it) and treats your JSON in the correct way, not as arbitrary text.
Give this a try:
token="$(sed -E -n -e 's/^.*access_token": ?"//p' <<<"$result" | cut -d'"' -f1)"
Explanation:
token="$( script here )" means that $token is set to the output/result of the script run inside the subshell through a process known as command substituion
-E in sed allows Extended Regular Expressions. We want this because JSON generally contains a space after the : and before the next ". We use the ? after the space to tell sed that the space may or may not be present.
<<<"$result" is a herestring that feeds the data into sed as stdin in place of a file.
I am trying to change the values in a text file using sed in a Bash script with the line,
sed 's/draw($prev_number;n_)/draw($number;n_)/g' file.txt > tmp
This will be in a for loop. Why is it not working?
Variables inside ' don't get substituted in Bash. To get string substitution (or interpolation, if you're familiar with Perl) you would need to change it to use double quotes " instead of the single quotes:
# Enclose the entire expression in double quotes
$ sed "s/draw($prev_number;n_)/draw($number;n_)/g" file.txt > tmp
# Or, concatenate strings with only variables inside double quotes
# This would restrict expansion to the relevant portion
# and prevent accidental expansion for !, backticks, etc.
$ sed 's/draw('"$prev_number"';n_)/draw('"$number"';n_)/g' file.txt > tmp
# A variable cannot contain arbitrary characters
# See link in the further reading section for details
$ a='foo
bar'
$ echo 'baz' | sed 's/baz/'"$a"'/g'
sed: -e expression #1, char 9: unterminated `s' command
Further Reading:
Difference between single and double quotes in Bash
Is it possible to escape regex metacharacters reliably with sed
Using different delimiters for sed substitute command
Unless you need it in a different file you can use the -i flag to change the file in place
Variables within single quotes are not expanded, but within double quotes they are. Use double quotes in this case.
sed "s/draw($prev_number;n_)/draw($number;n_)/g" file.txt > tmp
You could also make it work with eval, but don’t do that!!
This may help:
sed "s/draw($prev_number;n_)/draw($number;n_)/g"
You can use variables like below. Like here, I wanted to replace hostname i.e., a system variable in the file. I am looking for string look.me and replacing that whole line with look.me=<system_name>
sed -i "s/.*look.me.*/look.me=`hostname`/"
You can also store your system value in another variable and can use that variable for substitution.
host_var=`hostname`
sed -i "s/.*look.me.*/look.me=$host_var/"
Input file:
look.me=demonic
Output of file (assuming my system name is prod-cfm-frontend-1-usa-central-1):
look.me=prod-cfm-frontend-1-usa-central-1
I needed to input github tags from my release within github actions. So that on release it will automatically package up and push code to artifactory.
Here is how I did it. :)
- name: Invoke build
run: |
# Gets the Tag number from the release
TAGNUMBER=$(echo $GITHUB_REF | cut -d / -f 3)
# Setups a string to be used by sed
FINDANDREPLACE='s/${GITHUBACTIONSTAG}/'$(echo $TAGNUMBER)/
# Updates the setup.cfg file within version number
sed -i $FINDANDREPLACE setup.cfg
# Installs prerequisites and pushes
pip install -r requirements-dev.txt
invoke build
Retrospectively I wish I did this in python with tests. However it was fun todo some bash.
Another variant, using printf:
SED_EXPR="$(printf -- 's/draw(%s;n_)/draw(%s;n_)/g' $prev_number $number)"
sed "${SED_EXPR}" file.txt
or in one line:
sed "$(printf -- 's/draw(%s;n_)/draw(%s;n_)/g' $prev_number $number)" file.txt
Using printf to build the replacement expression should be safe against all kinds of weird things, which is why I like this variant.
set f_d "y"
exec sed {/feature $f_d starts/, /feature $f_d ends/ d} file > temp_file
I would like to use the value of f_d in the sed command but I'm not able to do that. Someone please help me with this.
The right tool is to use double-quoting instead of brace quoting.
exec sed "/feature $f_d starts/, /feature $f_d ends/ d" file > temp_file
BE AWARE that this means you may need to be very careful. In particular, if your real code has backslashes or other Tcl metacharacters in the sed script then you will need to quote those characters.
And you can do the task entirely in Tcl without calling any external programs.
I am trying pass value from TK to cshell script using "procedure call" now.... as follow.
proc Run {} {
global passedvalue
## to see what value it has for passedvalue
puts $passedvalue
exec sed -i {s/ABC/$passedvalue/g} runme.sh
exec /bin/csh -c ./runme.sh >#stdout 2>#stderr
}
I am changing a line which has value ABC by new passedvalue.
"puts" works and prints the value of passedvalue properly.
But it does not work for sed and it gives
Error : Program undefined variable
Please let me know how where I am doing wrong.
I have tried using string map as well but did work either...I might be doing something wrong.
Curly braces inhibit variable substitution. If you want $passedvalue to be expanded before calling exec, you'll need to use some other quoting mechanism.
For example, you could use double quotes:
exec sed -i "s/ABC/$passedvalue/g" runme.sh
You will need to add some extra bullet-proofing, however. For example, if $passedvalue Has a / in it, you will send a mal-formed expression to sed.