Evaluating or expanding a variable to get its value. Depending on the language, a variable may be expanded one or more times.
Questions tagged [variable-expansion]
246 questions
956
votes
7 answers
When do we need curly braces around shell variables?
In shell scripts, when do we use {} when expanding variables?
For example, I have seen the following:
var=10 # Declare variable
echo "${var}" # One use of the variable
echo "$var" # Another use of the variable
Is there a significant…
New User
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182
votes
8 answers
How does the Windows Command Interpreter (CMD.EXE) parse scripts?
I ran into ss64.com which provides good help regarding how to write batch scripts that the Windows Command Interpreter will run.
However, I have been unable to find a good explanation of the grammar of batch scripts, how things expand or do not…
Benoit
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134
votes
34 answers
What is the most elegant way to remove a path from the $PATH variable in Bash?
Or more generally, how do I remove an item from a colon-separated list in a Bash environment variable?
I thought I had seen a simple way to do this years ago, using the more advanced forms of Bash variable expansion, but if so I've lost track of it.…
Ben Blank
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109
votes
7 answers
How to obtain the first letter in a Bash variable?
I have a Bash variable, $word, which is sometimes a word or sentence, e.g.:
word="tiger"
Or:
word="This is a sentence."
How can I make a new Bash variable which is equal to only the first letter found in the variable? E.g., the above would…
Village
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75
votes
4 answers
How do SETLOCAL and ENABLEDELAYEDEXPANSION work?
I notice in most scripts, the two are usually in the same line as so:
SETLOCAL ENABLEDELAYEDEXPANSION
Are the two in fact separate commands and can be written on separate lines?
Will setting ENABLEDELAYEDEXPANSION have an adverse effect on a script…
Anthony Miller
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30
votes
6 answers
Performance of variable expansion vs. sprintf in PHP
Regarding performance, is there any difference between doing:
$message = "The request $request has $n errors";
and
$message = sprintf('The request %s has %d errors', $request, $n);
in PHP?
I would say that calling a function involves more stuff,…
elitalon
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30
votes
7 answers
Brace expansion with variable?
#!/bin/sh
for i in {1..5}
do
echo "Welcome"
done
Would work, displays Welcome 5 times.
#!/bin/sh
howmany=`grep -c $1 /root/file`
for i in {1..$howmany}
do
echo "Welcome"
done
Doesn't work! howmany would equal 5 as that is what the output of…
user2891460
26
votes
2 answers
Expand variable inside single quotes
How can I expand $pw inside single quotes?
$pw = "$PsHome\powershell.exe"
cmd.exe /c 'schtasks /create /tn cleanup /tr "$pw -WindowStyle hidden -ExecutionPolicy Bypass -nologo -noprofile %TEMP%\exec.ps1" /sc minute /mo 1'
Pedro Lobito
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19
votes
4 answers
get a default value when variable is unset in make
(edit: question more accurate based on @Michael feedback)
In bash, I often use parameter expansion: the following commands print "default value" when $VARNAME is unset, otherwise it prints the VARNAME content.
echo ${VARNAME:-default value} #if…
oHo
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16
votes
3 answers
bash send string argument as multiple arguments
So I have a bash script that is generating a string of commands that I want to be run. The output looks something like
$ program "command1 command2 ... commandN"
But the program is interpreting (as it should) "command1 command2 ... commandN" as one…
trev9065
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13
votes
2 answers
How to expand variables in vim commands?
I'm trying to get a variable expanded in a command call. Here's what I have in my .vimrc:
command! -nargs=1 -complete=dir TlAddPm call s:TlAddPm()
function! s:TlAddPm(dir)
let flist = system("find " . shellescape(a:dir) . " -type f -name…
derobert
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11
votes
5 answers
How do I delay expansion of variables in PowerShell strings?
Whatever you want to call it, I'm trying to figure out a way to take the contents of an existing string and evaluate them as a double-quoted string. For example, if I create the following strings:
$string = 'The $animal says "meow"'
$animal =…
Adi Inbar
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10
votes
1 answer
Passing a command with arguments as a string to docker run
The issue I'm facing is how to pass a command with arguments to docker run. The problem is that docker run does not take command plus arguments as a single string. They need to be provided as individual first-class arguments to docker run, such…
davidA
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9
votes
1 answer
What's wrong with the following GNU make shell variable expansion?
On this line:
GCCVER:=$(shell a=`mktemp` && echo $'#include \nmain() {printf("%u.%u\\n", __GNUC__, __GNUC_MINOR__);}' | gcc -o "$a" -xc -; "$a"; rm "$a")
I get:
*** unterminated call to function `shell': missing `)'. Stop.
What's wrong…
Matt Joiner
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9
votes
1 answer
What does "${!var}" mean in shell script?
I have a code block with below condition, not sure what exactly it does.
$var = "${args}_Some_Text"
if [ "${!var}" == '' ];then
echo "$var is not defined !!!"
fi
tempuser
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