All Questions
Tagged with bash shell-script
6,897 questions
659
votes
4
answers
506k
views
Using "${a:-b}" for variable assignment in scripts
I have been looking at a few scripts other people wrote (specifically Red Hat), and a lot of their variables are assigned using the following notation
VARIABLE1="${VARIABLE1:-some_val}"
or some expand ...
- 7,519
598
votes
4
answers
1.8m
views
In a bash script, using the conditional "or" in an "if" statement
This question is a sequel of sorts to my earlier question. The users on this site kindly helped me determine how to write a bash for loop that iterates over string values. For example, suppose that ...
- 17.6k
463
votes
18
answers
702k
views
How do I change the extension of multiple files?
I would like to change a file extension from *.txt to *.text. I tried using the basename command, but I'm having trouble changing more than one file.
Here's my code:
files=`ls -1 *.txt`
for x in $...
- 4,959
438
votes
16
answers
89k
views
In Bash, when to alias, when to script and when to write a function?
Noone should need 10 years for asking this question, like I did. If I were just starting out with Linux, I'd want to know: When to alias, when to script and when to write a function?
Where aliases are ...
- 13.5k
377
votes
6
answers
417k
views
Why does my shell script choke on whitespace or other special characters?
… or an introductory guide to robust filename handling and other string passing in shell scripts.
I wrote a shell script which works well most of the time. But it chokes on some inputs (e.g. on some ...
320
votes
12
answers
586k
views
How can I test if a variable is empty or contains only spaces?
The following bash syntax verifies if param isn't empty:
[[ ! -z $param ]]
For example:
param=""
[[ ! -z $param ]] && echo "I am not zero"
No output and its fine.
But when param is ...
- 7,221
318
votes
5
answers
405k
views
What is the meaning of IFS=$'\n' in bash scripting?
At the beginning of a bash shell script is the following line:
IFS=$'\n'
What is the meaning behind this collection of symbols?
- 27.5k
283
votes
15
answers
442k
views
Passing named arguments to shell scripts
Is there any easy way to pass (receive) named parameters to a shell script?
For example,
my_script -p_out '/some/path' -arg_1 '5'
And inside my_script.sh receive them as:
# I believe this notation ...
- 42.6k
279
votes
3
answers
56k
views
Security implications of forgetting to quote a variable in bash/POSIX shells
If you've been following unix.stackexchange.com for a while, you
should hopefully know by now that leaving a variable
unquoted in list context (as in echo $var) in Bourne/POSIX
shells (zsh being the ...
- 574k
243
votes
3
answers
171k
views
Are there naming conventions for variables in shell scripts?
Most languages have naming conventions for variables, the most common style I see in shell scripts is MY_VARIABLE=foo. Is this the convention or is it only for global variables? What about variables ...
- 5,541
232
votes
6
answers
482k
views
Can I redirect output to a log file and background a process at the same time?
Can I redirect output to a log file and a background process at the same time?
In other words, can I do something like this?
nohup java -jar myProgram.jar 2>&1 > output.log &
Or, is ...
- 4,257
207
votes
5
answers
469k
views
How do I add X days to date and get new date?
I have Linux ( RH 5.3) machine
I need to add/calculate 10 days plus date so then I will get new date (expiration date))
for example
# date
Sun Sep 11 07:59:16 IST 2012
So I need to get
...
yael
194
votes
7
answers
442k
views
How do I delete the first n lines of an ascii file using shell commands?
I have multiple files that contain ascii text information in the first 5-10 lines, followed by well-tabulated matrix information. In a shell script, I want to remove these first few lines of text so ...
- 9,773
181
votes
1
answer
80k
views
When is double-quoting necessary?
The old advice used to be to double-quote any expression involving a $VARIABLE, at least if one wanted it to be interpreted by the shell as one single item, otherwise, any spaces in the content of $...
- 16.2k
176
votes
4
answers
306k
views
How can I execute local script on remote machine and include arguments?
I have written a script that runs fine when executed locally:
./sysMole -time Aug 18 18
The arguments "-time", "Aug", "18", and "18" are successfully passed on to the script.
Now, this script is ...
- 2,497