All Questions
26,338
questions
375
votes
6
answers
409k
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 ...
281
votes
5
answers
74k
views
Why is using a shell loop to process text considered bad practice?
Is using a while loop to process text generally considered bad practice in POSIX shells?
As Stéphane Chazelas pointed out, some of the reasons for not using shell loop are conceptual, reliability, ...
- 155k
279
votes
10
answers
93k
views
Why *not* parse `ls` (and what to do instead)?
I consistently see answers quoting this link stating definitively "Don't parse ls!" This bothers me for a couple of reasons:
It seems the information in that link has been accepted wholesale with ...
- 58.7k
716
votes
4
answers
316k
views
Why is printf better than echo?
I have heard that printf is better than echo. I can recall only one instance from my experience where I had to use printf because echo didn't work for feeding some text into some program on RHEL 5.8 ...
- 12.6k
181
votes
1
answer
78k
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 $...
- 15.6k
275
votes
4
answers
53k
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 ...
- 554k
434
votes
3
answers
220k
views
What are the shell's control and redirection operators?
I often see tutorials online that connect various commands with different symbols. For example:
command1 | command2
command1 & command2
command1 || command2
command1 && command2
...
- 245k
219
votes
8
answers
41k
views
Why is looping over find's output bad practice?
This question is inspired by
Why is using a shell loop to process text considered bad practice ?
I see these constructs
for file in `find . -type f -name ...`; do smth with ${file}; done
and
for ...
- 83.5k
197
votes
6
answers
299k
views
How can we run a command stored in a variable?
$ ls -l /tmp/test/my\ dir/
total 0
I was wondering why the following ways to run the above command fail or succeed?
$ abc='ls -l "/tmp/test/my dir"'
$ $abc
ls: cannot access '"/tmp/test/my': No ...
- 103k
112
votes
1
answer
20k
views
Why does my regular expression work in X but not in Y?
I wrote a regular expression which works well in a certain program (grep, sed, awk, perl, python, ruby, ksh, bash, zsh, find, emacs, vi, vim, gedit, …). But when I use it in a different program (or on ...
490
votes
6
answers
93k
views
Why not use "which"? What to use then?
When looking for the path to an executable or checking what would happen if you enter a command name in a Unix shell, there's a plethora of different utilities (which, type, command, whence, where, ...
- 554k
156
votes
1
answer
118k
views
Understanding the -exec option of `find`
I find myself constantly looking up the syntax of
find . -name "FILENAME" -exec rm {} \;
mainly because I don't see how exactly the -exec part works. What is the meaning of the braces, the ...
- 1,687
1609
votes
10
answers
527k
views
What is the exact difference between a 'terminal', a 'shell', a 'tty' and a 'console'?
I think these terms almost refer to the same thing, when used loosely:
terminal
shell
tty
console
What exactly does each of these terms refer to?
- 35.6k
139
votes
4
answers
16k
views
Why are there so many different ways to measure disk usage?
When I sum up the sizes of my files, I get one figure. If I run du, I get another figure. If I run du on all the files on my partition, it doesn't match what df claims is used. Why are there so many ...
528
votes
9
answers
394k
views
Execute vs Read bit. How do directory permissions in Linux work?
In my CMS, I noticed that directories need the executable bit (+x) set for the user to open them. Why is the execute permission required to read a directory, and how do directory permissions in Linux ...
- 6,373