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Questions tagged [command-substitution]

Command substitution is the replacement of a command with the result returned after it is evaluated.

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How can I override a bash variable at the time of executing it in console?

I have a bash script that will print yesterdays date. It looks like this: #!/bin/bash YESTERDAY_DATE=$(date '+%Y-%m-%d' -d '1 day ago') echo $YESTERDAY_DATE and I can run it like: ./script.sh, output as follows: 2021-02-23 Now, I want to be…
Saffik
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indirect bash command execution not working as expected with coproc

I'm quite new to linux shell scripting and have a question: 1.) why does the command test1="leafpad" && coproc exec "$test1" work in bash (commandline, GNU bash 4.4.12 on a debian derivate linux), but the command test1="coproc" && exec "$test1"…
MI605
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find command written in bash script outputs command not found

#!/bin/bash 18 if [ "$arg" == "jpg" ] then 19 "$(find ./"$folder" -type f -name "*.jpg" -exec mv {} "$arg" \;)" 20 fi This block of code above works and the find and mv command executes and I have the output in the jpg folder but my script…
catBuddy
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fold: invalid number of columns when running script with arguments

I got a strange behavior when running a script with arguments that contains a command substitution. I would like to understand why is this behavior happening. The script is: #!/bin/bash # MAIL=$1 # USER=$2 PASSWORD=$(cat /dev/urandom | tr -dc…
Pulsar
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command substitution not working in alias?

I wanted to make an alias for launching a vim session with all the c/header/makefiles, etc loaded into the buffer. shopt -s extglob alias vimc="files=$(ls -A *.?(c|h|mk|[1-9]) .gitconfig [mM]akefile 2>/dev/null); [[ -z $files ]] || vim $files" When…
First User
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bash logic inside command substitution

I have a little banner that I display at login fignow() { figlet -w $(tput cols) $(date +"%b %d, Week %V"); figlet -w $(tput cols) -f univers $(date +"%H:%M"); } This works fine if the additional fonts are installed to get univers, but that's not…
YorSubs
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From all the files that their name is composed of 4 letters, which contain the string “user” in their content?

I have to answer this question as an exercise. Sample input: No sample, just trying to select and filter files using Unix shell according to some conditions Sample output: a list of files that their name is composed of 4 letters and which contain…
Ruben Cohen
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bash get back interpreted escape string

Consider the following bash script #!/usr/bin/env bash tstring="Hi\tThere" istring=$(echo -e $tstring) echo $istring # Prints: Hi There rstring=$(printf '%q' "$istring") # This is not doing what I intended echo $rstring # Prints: $'Hi\tThere' I…
Vikash Balasubramanian
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command to create file name with date as postfix using shell script

I need to create the dump file name with the current date as postfix to the file name in shell script. I tried below command in my script but that did not work. Can any one suggest me the way : ... dump_'$(date '+%Y-%m-%d')'.txt BACKGROUND: I feel…
jailaxmi k
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variable error in bash when doing calculation

I assigned output of piping into a variable, but when I try to use the variable to do math, it won't allow me: %%bash cd /data/ref/ grep -v ">" EN | wc -c > ref cat ref cd /example/ grep -v ">" SR | wc -l > sample cat sample echo $((x= cat sample,…
user432797
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How to use the output of one command as the bash completion for another

I'm creating a new command and I need a completion function so that when I press tab a couple of times it gives me some alternatives to choose from. The list of alternatives should be the branches available in a git repository. I've used complete -W…
Abdallah
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Issues passing variables inside of command substitution in bash

I want to run sort and pass LC_COLLATE=C to it. The output is then going to be stored in a variable. I wrote this: var="$(LC_COLLATE=C sort 'aaa Abc')" But, oddly enough, I receive sort: No such file or directory. I most definately have sort on my…
leetbacoon
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Using bash variable in input redirection with sort command

I have a bash script written as follows in Jenkins Execute shell block id="233" I want to use this id variable inside following command bash -c 'comm -12 <(sort file1_${id}.txt) <(sort file2_${id}.txt)' But it throws error sort: cannot read:…
hruday
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Run command substitution inside function when function is called

I have a bash script which have some helper function inside a shared, common file lib.sh. However, some of these functions look like this: function check_prs { local labels labels=$(hub pr show -h "${BRANCH:-}" -F '%L') if [[ $PRLABELS…
Christian P.
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Executing the output as filename

In one of my Bash scripts, there's a point where I have a variable SCRIPT which contains the /path/to/an/exe, and what the script ultimately needs to do, is executing that executable. Therefore the last line of the script is $($SCRIPT) so that…
Enlico
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