Questions tagged [variable-substitution]
The variable-substitution tag has no usage guidance.
1
vote
0answers
27 views
!$ vs $_ difference? [duplicate]
In GNU Bash, both !$ and $_ expands to the last argument of the last command.
I think they're identical and I need someone to tell me if there is any difference.
5
votes
5answers
597 views
Using parameter substitution on a Bash array
I have file.txt that I need to read into a Bash array. Then I need to remove spaces, double quotes and all but the first comma in every entry. Here's how far I've gotten:
$ cat file.txt
10,this
2 0 ...
2
votes
1answer
48 views
Combine brace and variable expansion in one line
I would like to have a logging function that takes filenames as arguments and replicate the stdout to all of these files. This is what I have come up so far:
function logger() {
exec > >(...
0
votes
0answers
48 views
Use variable inside sed command [duplicate]
how can i use variables inside this sed command?
sed -i.bak -e '/triggerword/,${w $DIR/tempfile' -e 'd;}' $DIR/targetfile
inside -e '{w $DIR/tempfile' -e 'd;}' the $DIR/tempfile isn't recognized
0
votes
1answer
42 views
why curl can't expand variable inside the loop, but echo can?
I need to include variable inside curl
for fname in "assets/*.drx"; do
echo $fname
curl -F file=@"$fname" "http://someurl.com/"
echo $fnamename
done
Result:
assets/...
10
votes
1answer
443 views
What does the substitution ${!var_name+x} mean?
I found a script that has a function that checks if a variable is set but i don't understand it very well.
check_if_variable_is_set() {
var_name=$1
if [ -z "${!var_name+x}" ]; then
...
0
votes
3answers
186 views
Modifying a shell variable with regex (bash)
I have a shell variable for example. a="big little man". How do I use regex in bash print out the variable with only the middle word capitalized? (big LITTLE man)
I can do it by separating the ...
0
votes
2answers
50 views
How can I export a variable in bash where the variable name is comprised of two variables?
I'm trying to export variables inside of a for loop where I wanted each iteration of the loop to change what variable was being written to. I've been looking for the right syntax to satisfy exporting ...
0
votes
1answer
142 views
Bad substitution when running from cron
I have a function (notify_dba) that with two string args, a header and a body. (correction) Works well from shell prompt, but not in cron Err, doesn't work in either shell or cron (but should...?):
...
2
votes
1answer
26 views
How can I build an env file (with $ characters) listing as-is from echo command?
I am trying to build a file invoked from a script that echoes what is in quotes to a file - only, the $ gets omitted.
This is what I was trying to do:
echo -e "export ORACLE_BASE=/oracle/APP/grid \n ...
0
votes
0answers
13 views
Interaction of sed and for loop [duplicate]
for i in {1..25}; do cat file$((i)) | sed 's/.*/$((i))/'; done
doesn't print the current value of i but just $((i)). How can I make it print the value of i instead?
0
votes
2answers
60 views
Running multiple command against files matching a brace+glob pattern without repeating it
I would like to run a series of commands against a set of files matched by a braces-and-globs pattern, without copy-pasting the pattern all over the place. I've been trying to do this by putting the ...
1
vote
1answer
31 views
Zsh: check existing of file before expanding
In Zsh parameter expansion, I have:
"${test_var:-"${HOME}/test"}"
but here I want to check if ${HOME}/test is exist or not, if not exist then test_var expand to " " (one space string).
Is there an ...
5
votes
0answers
78 views
Correct treatment of quotes in parameter expansions
Using the default value of IFS, consider
unset var
set -- ${var:-"hello"}
echo "$#"
This prints 1 as the parameter expansion expands to the single string hello.
unset var
set -- "${var:-"hello"}"
...
0
votes
1answer
29 views
Can variable-substitution-syntaxes be unified?
Can these two variable-substitution-syntaxes combined into one?
rm "$s_a/$domain.conf" 2>/dev/null
rm "$s_e/$domain.conf" 2>/dev/null
like:
rm "$s_{a,e}/$domain.conf" 2>/dev/null
1
vote
1answer
722 views
using variables inside the curl command not working in bash script
I am trying to write a bash script to update certain nodes in my repository. I wrote below script, but it does not seem to be working when I use variables inside curl. Below is the code. I tried all ...
3
votes
2answers
287 views
Bash parameter substituiton within commands
I have a passing understanding of Parameter Substitution, including substrings like so
foo="Hello World";
greeting=${foo:0:6}
But do I do this with commands?
greeting="Hello"
md5greeting=$(echo $...
3
votes
4answers
639 views
awk - replace number greater than 17 digits in a column with -
I have a CSV file containing timestamp values in UTC which I need to replace with -. There may be more than one timestamp in the same column, can you please let me know how do I do that?
For example, ...
0
votes
4answers
41 views
substitutions in vi editor
I have file called foo.txt. This file contains values:
abc.tar.gz
abc.1.1.tar.gz
bca-1.2.tar.gz
I would like to get an output like this
abc abc.tar.gz
abc.1.1 abc.1.1.tar.gz
bca-1.2 bca-1.2.tar.gz
...
1
vote
1answer
240 views
Makefile: Copy using make variables --> error; Not so without variables!
In the following makefile
InputLocation:=./Test
OutputLocation:=$(InputLocation)/Output
Input:=$(wildcard $(InputLocation)/*.md)
Output:=$(patsubst $(InputLocation)/%, $(OutputLocation)/%, $(Input:...
0
votes
2answers
33 views
How do I append a date to a file using Bash script with multiple variables?
My script is below, I can't remember how to make this make sense.
#!/bin/bash
input=$1
output=$2
cp $input $output_$(date +%m%d%y)
The goal is to run the script as follows
/path/script.sh /path/...
1
vote
3answers
126 views
Dynamic variables in shell
I have a following script that will take input (source path) from user and it will attach the volume inside docker container
echo -n "Enter the source path: "
read path
docker run -v $path:/opt/$...
1
vote
1answer
418 views
Glob character within variable expands in bash but not zsh
I'm seeing an issue with zsh where a glob character within a variable is not expanding as I would expect. The following example does a better job of explaining it.
$ echo $0
-bash
$ echo $HOME/...
0
votes
2answers
95 views
Using shell 'printf' where the format string is in a variable and doesn't have a fixed number of field placeholders?
I am writing a shell function which makes an external API call via cURL (the external API syntax isn't under my control). I've approached it like this (simplified):
#!/bin/sh
template_get_entry='...
0
votes
2answers
547 views
Passing an argument with double and single quotes to another call in bash [closed]
I have a call
./run.sh name --vars="service_name='someothername'"
and I'm trying to call another program with exactly same --vars="service_name='someothername'" argument from run.sh, however when ...
13
votes
4answers
2k views
Is it possible to print the content of the content of a variable with shell script? (indirect referencing)
Let's suppose I've declared the following variables:
$ var='$test'
$ test="my string"
If I print their contents I see the following:
$ echo $var
$test
$ echo $test
my string
I'd like to find a ...
1
vote
0answers
115 views
Bash variable value partially substituted in Curl input
Below is my shell script in which I'm trying to use the value of a variable as input to curl. However, the script is giving an error and when trying to debug the script, I can see that the value of ...
5
votes
3answers
236 views
How to create a loop with five (5) input variables?
I have a proprietary command that requires five (5) inputs to properly execute the command.
command -cval <value> -tval <value> -dval <value> -kval <value>
I need to be able ...
0
votes
2answers
336 views
${p:2:1} Meaning in the shell script
Can anyone tell me the meaning of ${p:2:1} in shell scripting as in:
var1=""
for p in [1,2,3,4]
do
var1="${var1} ${p:2:1}"
done
2
votes
0answers
66 views
What are the contexts where Bash doesn't perform word splitting and globbing?
Bash doesn't perform word splitting in globbing in these cases:
LHS or RHS of an assignment, except for indexed arrays
var=$value # simple variable
declare -A hash
key=...
0
votes
2answers
72 views
for loop variable assignment with whitespaces
Im collecting the LPAR names and assigning to a variable on AIX , Then using multiple commands for processing.
LPAR Names on the system are : ABCD56777 TSM Mobile CD CPT 2
for lparname in `...
7
votes
2answers
930 views
calling other variables in a variable name (Bash)
At the moment I have the next paths
langs="EN GE"
dir_EN=/xx
dir_GE=/zz
As you can see the variable $langs has all possible languages in a single array. I would like to save all those paths in a ...
0
votes
2answers
59 views
Automating wp-config.php creation
I use Ubuntu 16.04 with Bash and I tried to run the following command set to automatically create a WordPress wp-config.php file with the WordPress Bash extension WP-CLI. Yet I'm having some problem I ...
0
votes
3answers
35 views
Variable in variable expansion
I want to evaluate a variable, whose name will need to dynamically evaluate another varuiable, i.e. the var ENVIRONMENT can be either prod, stg, or test, so I have 3 urls:
URL_PROD=https://...
0
votes
1answer
170 views
Variable Expansion Adding Braces to Original String Value [closed]
NOTE: I missed a syntax issue in my script that was causing this. I was passing ${bar} as {$bar}. This can be removed or locked or whatever is done with these types of questions.
I'm trying to test ...
3
votes
2answers
75 views
Using variable values defined in one file, in files in the same directory
In this GitHub repository I have a directory named nwsm. This directory contains the file nwsm.sh that contains a master script (a script that runs other scripts).
The directory also contains a few ...
1
vote
1answer
182 views
Basic usage of /etc/cron/ (d): correct pattern for /etc/cron (daily/weekly/monthly)
I use Ubuntu 16.04 with Bash and I've created this extensionless, shebangless file /etc/cron.daily/cron_daily:
for dir in "$drt"/*/; do
if pushd "$dir"; then
wp plugin update --all --allow-root
wp ...
0
votes
0answers
40 views
Variable expansion succeeds with echo but fails without a command (execution by expansion) [duplicate]
I created a file nano ~/uncwe/configurations/variables.sh. This file contains:
set -a
rse="~/${repo}/internal_software/rse.sh"
set +a
I sourced the file, then tried to execute:
${rse}
bash ${rse}
...
1
vote
3answers
282 views
Trivial rm -rf command destroys my operating system in a testing machine
I use Bash 4.3.48(1) and I ran the following command pattern on a testing VPS machine:
rm -rf ${drt}/${pma}*
This command deleted the entire operating system (Ubuntu). That was evident by executing ...
3
votes
2answers
275 views
cat-redirect a file, but with variable expansions
I have the file ~/nginx_app containing this conf template:
server {
root /var/www/html/${domain}/;
server_name ${domain} www.${domain};
}
I also have this script:
#!/bin/bash
domain="$1" &...
0
votes
3answers
2k views
Reference bash variable from a variable [duplicate]
How can I reference a variable in bash based on another variable? Let me setup the example:
package="foobar"
# the variable I wish to reference is $foobar_darwin_amd64
# thus trying:
echo "$...
9
votes
9answers
3k views
Bash: Extract one of the four sections of an IPv4 address
We can use the syntax ${var##pattern} and ${var%%pattern} to extract the last and first section of an IPv4 address:
IP=109.96.77.15
echo IP: $IP
echo 'Extract the first section using ${var%%pattern}: ...
4
votes
4answers
3k views
Backslash in variable substitution in Bash
I was working on a Bash script to help partition a hard drive correctly, and I came across a strange problem where I had to append a number to a variable. It took me a while to get the outcome right ...
3
votes
1answer
758 views
Double Quotes in Bash's variable substitution
I am trying to configure some software packages with a script thereby I got the following problem. Assume that the environment variable PREFIX is set to the location where I plan to install the ...
4
votes
2answers
882 views
How does Bash handle quoting in the string replacement section of parameter expansion?
Is there any consistent logic to it?
some-command "${somevariable//some pattern/'how does this get parsed?'}"
I've posted some conclusions and raw tests below as an "answer" but they're not a full ...
1
vote
1answer
388 views
Run cd with path variable in bash script not working [duplicate]
When i run the script:
#!/bin/bash
DRUPAL_ROOT=$(drush status root --format=list)
if [ -z $DRUPAL_ROOT ]
then
echo -e "Not exists Drupal core"
else
echo $DRUPAL_ROOT
cd $DRUPAL_ROOT
fi
Output:
...
-1
votes
1answer
514 views
Variable won't get expanded when INSIDE mysql shell
Before creating a new mysql user and DB, I did:
read sps -s
# Inputing and saving the sps (password) value.
echo ${sps}
# sps password value echoed.
mysql -u root -p[PASSWORD]
mysql>...
1
vote
3answers
92 views
How to dynamically create Bash code with a loop and execute it as it is created
I have a list of lines in a Bash script as follows
if [ ! -z "$clone01" ]; then git clone "$clone01"; fi
if [ ! -z "$clone02" ]; then git clone "$clone02"; fi
if [ ! -z "$clone03" ]; then git clone "$...
2
votes
1answer
1k views
How can I change a Bash variable name in a loop and then expand the changed name?
I'm trying to expand variables Bash. I've searched but am not sure what the search terms are for what I am trying to do.
Here is my code.
Two questions:
How do I get the desired output as shown?
...
7
votes
1answer
569 views
Word splitting in positional parameters
Consider the following example:
IFS=:
x="a :b" # three spaces
echo ["$x"] # no word splitting
# [a :b] # as is
echo [$x] # word splitting
# [a b] # four spaces
Word splitting ...
