9,012 questions
343
votes
4
answers
194k
views
When to wrap quotes around a shell variable?
Should or should I not wrap quotes around variables in a shell script?
For example, is the following correct:
xdg-open $URL
[ $? -eq 2 ]
or
xdg-open "$URL"
[ "$?" -eq "2"...
- 7,257
963
votes
7
answers
475k
views
Difference between single and double quotes in Bash
In Bash, what are the differences between single quotes ('') and double quotes ("")?
- 33.9k
6278
votes
66
answers
5.2m
views
How do I execute a program or call a system command?
How do I call an external command within Python as if I had typed it in a shell or command prompt?
- 64.6k
2507
votes
16
answers
3.1m
views
How do I set a variable to the output of a command in Bash?
I have a pretty simple script that is something like the following:
#!/bin/bash
VAR1="$1"
MOREF='sudo run command against $VAR1 | grep name | cut -c7-'
echo $MOREF
When I run this script from the ...
- 25.5k
179
votes
7
answers
476k
views
I just assigned a variable, but echo $variable shows something else
Here are a series of cases where echo $var can show a different value than what was just assigned. This happens regardless of whether the assigned value was "double quoted", 'single quoted' or ...
- 125k
416
votes
7
answers
746k
views
How do I use shell variables in an awk script?
I found some ways to pass external shell variables to an awk script, but I'm confused about ' and ".
First, I tried with a shell script:
$ v=123test
$ echo $v
123test
$ echo "$v"
123test
Then tried ...
- 4,153
1919
votes
11
answers
887k
views
Difference between sh and Bash
When writing shell programs, we often use /bin/sh and /bin/bash. I usually use bash, but I don't know what's the difference between them.
What's the main difference between Bash and sh?
What do we ...
- 19.3k
169
votes
9
answers
57k
views
Useless use of cat?
This is probably in many FAQs - instead of using:
cat file | command
(which is called useless use of cat), correct way supposed to be:
command < file
In the 2nd, "correct" way - OS does not have ...
- 9,234
323
votes
6
answers
109k
views
Correct Bash and shell script variable capitalization
I run across many shell scripts with variables in all caps, and I've always thought that there is a severe misunderstanding with that. My understanding is that, by convention (and perhaps by ...
- 74k
729
votes
6
answers
481k
views
Command not found error in Bash variable assignment
I have this script called test.sh:
#!/bin/bash
STR = "Hello World"
echo $STR
when I run sh test.sh I get this:
test.sh: line 2: STR: command not found
What am I doing wrong? I look at extremely ...
- 91.8k
1487
votes
25
answers
2.0m
views
Running shell command and capturing the output
I want to write a function that will execute a shell command and return its output as a string, no matter, is it an error or success message. I just want to get the same result that I would have ...
- 46.3k
3032
votes
40
answers
3.9m
views
How do I split a string on a delimiter in Bash?
I have this string stored in a variable:
IN="[email protected];[email protected]"
Now I would like to split the strings by ; delimiter so that I have:
ADDR1="[email protected]"
ADDR2="[email protected]"
I don't ...
- 80.5k
2273
votes
21
answers
1.9m
views
How do I iterate over a range of numbers defined by variables in Bash?
How do I iterate over a range of numbers in Bash when the range is given by a variable?
I know I can do this (called "sequence expression" in the Bash documentation):
for i in {1..5}; do ...
- 23.6k
115
votes
10
answers
132k
views
How to print lines between two patterns, inclusive or exclusive (in sed, AWK or Perl)?
I have a file like the following and I would like to print the lines between two given patterns PAT1 and PAT2.
1
2
PAT1
3 - first block
4
PAT2
5
6
PAT1
7 - second block
PAT2
8
9
PAT1
10 - ...
- 294k
39
votes
2
answers
15k
views
Why is testing "$?" to see if a command succeeded or not, an anti-pattern?
I see here that testing whether $? is zero (success) or something else (failure) is an anti-pattern, but I have not been able to find this anywhere else.
Sticking to the definition of anti-pattern of ...
- 493