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This is about the Unix utility "test," also invoked as "[", or its shell syntax [[ … ]] variant. For questions about testing software and setups, use the "testing" tag.

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PostfixAdmin installed successfully. To test whether internal sending and receiving mail work, I used SMTP to send mail: telnet mail.example.com 25 Trying 94.284.174.110... Connected to mail.example....
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In the old times of DOS batch scripts, the only way to check for a variable to be empty or to allow an empty variable was to prepend (or append) a known letter, commonly the letter x, because there ...
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Continuing Semicolon in conditional structures (which handles single brackets), what's the point of having a semicolon after the closing DOUBLE bracket ]]? In my tests, running #!/bin/zsh -- if [[ &...
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When I run the following code declare -A X # get an associative array index="a'b" # a somewhat weird index X[$index]="this is set" echo "<<${X[$index]}>>" if ...
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Extremely "noob" question: I have a running sudo memtester ... on an Ubuntu 22.04 machine, but I gave it too much memory to test and it's taking too much time (I see it running and updating, ...
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I'm trying to check if the value inside a file is "0". COUNT_EXECUTION=$(< /tmp/count) if [ "$COUNT_EXECUTION" == "0" ]; then echo "Try restart service." ...
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I want to test if the output of a function matches the text I envision it should write to standard output. But the code below never prints test PASS and I can't figure out why. I also tried putting ...
branco's user avatar
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Here's what I'm trying to do (in a script): #!/usr/bin/env bash if [[ ! $("/usr/bin/scp [email protected]:/Users/seamus/Downloads/imgutils/image-utils* /home/pi/testscp") ]]; then ...
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I'm currently building Linux From Scratch 12.1 with the book, I've followed the instructions line by line. I'm struggling with the GCC testsuite, I have lots of FAIL and timeout. In addition to that, ...
noxen's user avatar
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I have following in a bash script: echo "status: [$status] and message: [$message]" if [ "${status}" -eq 0 && "$message" = "ERROR" ]; then echo &...
Nullpointer's user avatar
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From man bash: -n string True if the length of string is non‐zero. Examples: # expected $ var=""; [ -n "$var" ]; echo $? 1 # unexpected? $ var=""; [ -n $var ]; echo ...
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If I have /mydir/myfile.txt this code echos file already exists if [ ! -f "/mydir/myfile.txt" ]; then touch "/mydir/myfile.txt" echo "created file" else echo ...
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I have setup a little script to illustrate my problem. I have set up a while loop that I would like to keep looping as long as $output is equal to No screen session found #!/bin/bash echo Stopping ...
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I am relatively new to shell, and I am getting a syntax error where I am still confused. #!/bin/dash ls="ls -l test" small=0 medium=0 large=0 for i in $(seq 11 9 56) do filename=$(echo ...
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I want to determine all broken symlinks within a directory. In ignorance of a better solution, I tried this simple bash one-liner (bash version is 4.2.46, which may be worth mentioning because it's a ...
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I'm struggling with files and directory permissions. ls -l is telling me something that test -w contradicts. $ ls -l total 1792 -rw-r--r-- 1 root www-data 168 Jan 29 23:53 CODE_OF_CONDUCT.md -rw-...
rhommet's user avatar
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I am currently working in a project which is Linux based. From Linux terminal I have connected to our web application. The web application consists of pages and data in it so from Linux terminal I use ...
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There may be a duplicate somewhere (I guess), but I didn't find it so: Why do I see in some scripts those kind of tests: if [ x"$quiet_boot" = x0 ] with an x added before the actual ...
Totor's user avatar
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If there are spaces around the operator, test returns the correct value of the expression. But if there are no spaces, it doesn't throw any syntax error and always return true. $ test "A" == ...
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I am new at unix, I'm trying to learn the bash language, and when I went to the "Testing expression", I found this one: [[ "whatever" =~ h[aeiou] ]] I already read the answer to ...
andr.lex's user avatar
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I have a hardware watchdog, what is a good way to test that it actually works? Is there a standard script or such to set my system in an infinite loop to hog all resources or such to the point of ...
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I am doing a basic question for adding, product, subsraction, division by taking user input in first and second I don't understand where am I going wrong because it's not passing any test case. ...
Prince's user avatar
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I need to check that a directory (let's call it dir) contains one of two files (let's call them filea and fileb), but neither none nor both. The ideal solution would be to use a XOR operation between ...
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For the sake of this question, assume that the glob /a/b/c/* produces no matches. This means that the following test should fail (in other words, it should produce a non-zero $?): [[ -n /a/b/c/*(#qN) ]...
kjo's user avatar
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I just wanted to understand the meaning of the following statement and whether they seem correct. test -x /usr/bin/find || exit 0 Command 1 Command 2 Command 3 The output of test -x /usr/bin/find is ...
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First I follow this answer then I search about test -v then https://linuxcommand.org/lc3_man_pages/testh.html shows that there is an R option. test -R seems related to name preference. Then I search ...
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In bash, the conditional expression with the unary test -v myvariable tests wether the variable myvariable has been set. Note that myvariable should not be expanded by prefixing it with a dollar, so ...
db-inf's user avatar
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I'm perplexed but still guess I misunderstood Bash somehow. /$ if [ -e /bin/grep ]; then echo yea; else echo nay ; fi yea /$ if [ ! -e /bin/grep ]; then echo yea; else echo nay ; fi nay /$ if [ -a ...
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I'm trying to detect if a process (goland.sh) is running. I used this: #!/bin/bash if pgrep "goland.sh" >/dev/null 2>&1 ; then echo "running" exit 1 fi echo &...
Dean's user avatar
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Consider the following: echo "hello" > file.txt is_match1 () { local m m=$(cat "file.txt" | grep -F "$1") if [ -z "$m" ]; then return 1 fi } ...
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In a dockerized Alpine 3.14.2 running Bash 5.1.4(1), I encountered a strange behaviour in a Bash script. The essential line is a test for executability of a file, which always fails. This is the if ...
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If i want to combine the -a and -o script operators in an if statement, how could I do that? For example: if [ ( -e file.txt -a -r file.txt ) -o ( -e file2.txt -a -r file2.txt ) ]; then .... fi Can I ...
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I am using solutions from Test if a command outputs an empty string. In addition to those solutions, I want to print command's output if its not empty. I was wondering would it be possible to print ...
alper's user avatar
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3 answers
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When I try the following expression in bash I get a strange error message: [: -lt: unary operator expected First the function definition some_func () { (( 3 + 5 )) } And the expression [ $(...
von spotz's user avatar
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1 answer
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I am trying to create a simple bash script to read user input and use this input as a variable within my script. It currently looks like this : echo "Please specify file:" read FILE What I ...
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2 votes
1 answer
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I have a book that stated: "....For example, if the shell variable symbol contains an equal sign, look at what happens if you try to test it for zero length: $ echo $symbol = $ test -z "$...
Jacky's user avatar
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I need to test if an input it has the fromat of a car plate (0000-XYZ) and from the japanese ZIP wich the format is 000-0000
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1 answer
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I am attempting to do a comparison before I append conditions to a profile.d file A grep -F 'TMOUT' /etc/profile.d/sh.local shows me exactly what I expect however the test is always showing true. In ...
MikeG's user avatar
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1 answer
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I am writing a bash script to makup the MariaDB instance on a Synology box. When I run it, it works, but I get an error: admin@synology:/volume1/@appstore/MariaDB10/usr/local/bip$ ./mysql_backup ./...
symcbean's user avatar
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I am relatively new to shell (just now the basics of it). I am trying to make sense of a script in order to fix a bug and I stumble upon something that I can't find an answer through Google(probably ...
joeCarpenter's user avatar
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1 vote
2 answers
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I am new to Gnu/Linux and bash, and I am trying, unsuccessfully, to write a simple bash script to test if date +%H is within a predefined range of hours. Example: hour='date +%H' if [[ $hour -ge 12 ]] ...
tigger's user avatar
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I have a self written script like (./myscript) and I want to call some commands in that script. So I want to learn how to inject commands into a shell script like this one: #!/bin/bash set -x if ...
MrPython's user avatar
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I'm looking for preferably a one-liner that drops a directory tree a few layers deep with files that contain "realistic" data, as in, not /dev/zero nor /dev/urandom. Data that noticeably ...
Daffy's user avatar
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I got plenty possible variables in a form of [a-z][0-9], eg 1 letter and 1 number. Is there a way to test them in dash? Something like: myvar=o7 if [ $myvar=o[0-4] ]; then "do this" elif [ $...
user avatar
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3 answers
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I'm trying to compare the state of more than two variables. The use-case is a script that, among other options, should select (or auto-select) only one of several "modes" based on available ...
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4 votes
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Is it possible to have a conditional within /etc/rc.local? I've checked many Q&As and most people suggest running chmod +x on it, but my problem is different. It actually does work for me without ...
aderchox's user avatar
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Single square brackets [ and testcommand both are built in the bash shell. Why are there two separate commands if both square brackets [ and test commands have the same function?
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In bash programming I've always defined conditional variables in the following long hand way dog=1 if [[ $dog -eq 1 ]] ; then cow=1 else cow=0 fi This is obviously incredibly inefficient. In ...
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3 answers
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Is there a way to use a Filename Expansion within a test expression, more specifically, a bash conditional expression? For example: [[ -f foo* ]] && echo 'found it!' || echo 'nope!'; ... will ...
Ricardo's user avatar
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3 votes
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I am learning the zsh in the conditional expressions part, and I found some unreasonable output. For example: $ mkdir emptyspace && cd emptyspace $ var_assigned_with_emptystring="" $...
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