447
votes
Accepted
How can I get the current working directory?
There's no need to do that, it's already in a variable:
$ echo "$PWD"
/home/terdon
The PWD variable is defined by POSIX and will work on all POSIX-compliant shells:
PWD
Set by the shell ...
- 219k
145
votes
Accepted
Replace environment variables in a file with their actual values?
You could use envsubst (part of gnu gettext):
envsubst < infile
will replace the environment variables in your file with their corresponding value. The variable names must consist solely of ...
- 73.9k
141
votes
How to exit a shell script if one part of it fails?
One approach would be to add set -e to the beginning of your script. That means (from help set):
-e Exit immediately if a command exits with a non-zero status.
So if any of your commands fail, ...
- 219k
140
votes
Accepted
Easy command line method to determine specific ARM architecture string?
On Debian and derivatives,
dpkg --print-architecture
will output the primary architecture of the machine it’s run on. This will be armhf on a machine running 32-bit ARM Debian or Ubuntu (or a ...
- 365k
130
votes
Is there a unix command that gives the minimum/maximum of two numbers?
If you know you are dealing with two integers a and b, then these simple shell arithmetic expansions using the ternary operator are sufficient to give the numerical max:
$(( a > b ? a : b ))
and ...
- 8,031
117
votes
Accepted
How to get whole command line from a process?
You could use the -o switch to specify your output format:
$ ps -eo args
From the man page:
Command with all its arguments as a string. Modifications to the arguments may be shown. [...]
You may ...
- 14.6k
100
votes
Accepted
Bash throws error, line 8: $1: unbound variable
set -u will abort exactly as you describe if you reference a variable which has not been set. You are invoking your script with no arguments, so get_percent is being invoked with no arguments, ...
- 68.6k
93
votes
Confusing use of && and || operators
Here's my cheat sheet:
"A ; B" Run A and then B, regardless of success of A
"A && B" Run B if A succeeded
"A || B" Run B if A failed
"A &" Run A in background.
- 1,141
92
votes
How to grep for same string but multiple files at the same time?
grep -E 'fatal|error|critical|failure|warning|' *.log
- 4,480
91
votes
Accepted
Copy image from clipboard to file
You can actually do this with xclip using -t option.
See what targets are available:
$ xclip -selection clipboard -t TARGETS -o
TARGETS
image/png
text/html
Note the image/png target; go ahead and ...
- 103k
86
votes
Accepted
$@ except the 1st argument
First, note that $@ without quotes makes no sense and should not be used. $@ should only be used quoted ("$@") and in list contexts.
for i in "$@" qualifies as a list context, but here, to loop over ...
- 475k
77
votes
Accepted
shell find -delete "directory not empty"
As @Stephen Kitt mentions, this is largely a duplicate of find -delete does not delete non-empty directories which states that you're telling it to delete directories, but the directories aren't empty ...
- 1,568
76
votes
Accepted
What's a good mnemonic for shell double vs. single quotes?
Single quotes are simple quotes, with a single standard: every character is literal.
Double quotes have a double standard: some characters are literal, others are still interpreted unless there's a ...
71
votes
Multiple arguments in shebang
Although not exactly portable, starting with coreutils 8.30 and according to its documentation you will be able to use:
#!/usr/bin/env -S command arg1 arg2 ...
So given:
$ cat test.sh
#!/usr/bin/...
- 1,140
62
votes
Bash shell script output alignment
Use printf to format output (it's also more portable than echo). I would also store the real value of the colour escape sequences instead of storing them in a form that requires expansion by echo.
...
- 475k
61
votes
Accepted
Add path to $PATH if not already in $PATH
First check if the path to add is already part of the variable:
[[ ":$PATH:" != *":/path/to/add:"* ]] && PATH="/path/to/add:${PATH}"
If /path/to/add is already in the $PATH, then nothing ...
- 45.8k
58
votes
Accepted
Using the setuid bit properly
The setuid bit can be set on an executable file so that when run, the program will have the privileges of the owner of the file instead of the real user, if they are different. This is the difference ...
- 83k
56
votes
Automated ssh-keygen without passphrase, how?
The simplest way I found to do what you want is this (example using default filename)
< /dev/zero ssh-keygen -q -N ""
If the ~/.ssh/id_rsa file already exists, the command will exit ...
- 711
54
votes
Accepted
How do I replace AND (&&) in a for loop?
The equivalent to your original sequence would be:
for i in {1..20}
do
cmd $i || break
done
The difference with Amit's answer is the script won't exit, i.e. will execute potential commands that ...
- 58.3k
52
votes
Accepted
Bash multiplication and addition
Using arithmetic expansion:
for (( k = 0; k < 50; ++k )); do
a=$(( 2*k + 1 ))
echo "$a"
done
Using the antiquated expr utility:
for (( k = 0; k < 50; ++k )); do
a=$( expr 2 '*' "$k" + 1 ...
- 276k
51
votes
Accepted
How do I find the line number in Bash when an error occured?
Rather than use your function, I'd use this method instead:
$ cat yael.bash
#!/bin/bash
set -eE -o functrace
file1=f1
file2=f2
file3=f3
file4=f4
failure() {
local lineno=$1
local msg=$2
echo ...
slm♦
- 348k
50
votes
Bash shell script output alignment
Simply with column command:
yourscript.sh | column -t
The output:
Network 10.x.xx.xxx : Online
Network 10.x.xx.xxx : Offline
Network 10.x.xx.xxx : Offline
Network 10.x.xx.xxx ...
- 28.7k
50
votes
Accepted
How to run ssh command until succeeded?
Another option would be to use until.
until ssh me@device.local; do
sleep 5
done
If you do this repeatedly for a number of hosts, put it in a function in your ~/.bashrc.
repeat()
{
read -p "...
- 8,511
48
votes
Accepted
How do I extract the content of quoted strings from the output of a command?
Using grep + sed
This will parse the contents of those 2 strings:
$ grep -o '".*"' somefile | sed 's/"//g'
arch
arch2
The above looks for a string matching the pattern ".*". That will match ...
slm♦
- 348k
47
votes
How can I get the current working directory?
dir=$(pwd)
This is more portable and preferred over the backticks method.
Using $() allow you to nest the commands
eg : mech_pwd=$(pwd; echo in $(hostname))
- 1,191
47
votes
Accepted
At sign after shebang?
This looks like a placeholder in an GNU Automake template which is going to be filled in by a configure script. So it's neither a Perl or Unix kernel thing, but a GNU autotools thing.
It is probably ...
- 276k
47
votes
How to run a script every 64 hours?
Just run every hour and check that the number of hours since some arbitrary instant (for instance, instant 0 of the Unix epoch time) is a multiple of 64:
0 * * * * t=$(date +\%s); [ "$(( (t / ...
- 475k
46
votes
Accepted
Multiple arguments in shebang
There is no general solution, at least not if you need to support Linux, because the Linux kernel treats everything following the first “word” in the shebang line as a single argument.
I’m not sure ...
- 365k
46
votes
Using Python in a Bash Script
To run a set of Python commands from a bash script, you must give the Python interpreter the commands to run, either from a file (Python script) that you create in the script, as in
#!/bin/bash -e
# ...
- 276k
45
votes
Accepted
Replace character X with character Y in a string with bash
So many ways, here are a few:
$ string="a,b,c,d,e"
$ echo "${string//,/$'\n'}" ## Shell parameter expansion
a
b
c
d
e
$ tr ',' '\n' <<<"$string" ## With "tr"
a
b
c
d
e
$ sed 's/,/\n/g' &...
- 51.3k
Only top scored, non community-wiki answers of a minimum length are eligible