282
votes
Accepted
Split string by delimiter and get N-th element
Use cut with _ as the field delimiter and get desired fields:
A="$(cut -d'_' -f2 <<<'one_two_three_four_five')"
B="$(cut -d'_' -f4 <<<'one_two_three_four_five')"
You can also use ...
- 54.2k
92
votes
How to color diff output?
diff --color option was added to GNU diffutils 3.4 (2016-08-08)
This is the default diff implementation on most distros, which will soon be getting it.
Ubuntu 18.04 has diffutils 3.6 and therefore has ...
74
votes
Accepted
How to get the current date and time in YYYYMMDDHHMMSS format in ksh88?
I believe this is the command you need:
date '+%Y%m%d%H%M%S'
- 3,568
57
votes
Accepted
What's wrong with var=$(</dev/stdin) to read stdin into a variable?
(and no, for once, this is not about the missing quotes around $(...)¹).
The $(<file) operator
That Korn shell operator (also supported by zsh and bash) is described at length at Understanding Bash&...
- 513k
56
votes
Split string by delimiter and get N-th element
Wanted to see an awk answer, so here's one:
A=$(awk -F_ '{print $2}' <<< 'one_two_three_four_five')
B=$(awk -F_ '{print $4}' <<< 'one_two_three_four_five')
Try it online!
- 918
42
votes
Preferred syntax for two lines long pipe
Ask your self what would this do?
command1 \
| command2
Can't see the difference. Neither can I, but the shell can.
Look closely, there is a space after the \. This stops the newline from being ...
- 27.2k
40
votes
Split string by delimiter and get N-th element
Using only POSIX sh constructs, you can use parameter substitution constructs to parse one delimiter at a time. Note that this code assumes that there is the requisite number of fields, otherwise the ...
36
votes
Is the shell ksh93 dead?
It is not possible to give a real answer to this question, but the form of a comment is not sufficient. So I think it may be a good idea to collect points to a editable answer...
Two years ago, David ...
- 18.6k
29
votes
Is for(( ... )){ ... ;} a valid shell syntax? In which shells?
{ ...; } was already accepted in place of do ...; done in for loops in the first version of the Bourne shell in Unix V7 in the late 70s (see the source code) though never documented as far as I know.
...
- 513k
28
votes
How to color diff output?
If you have access to GNU diff you can use its --X-group-format options to get that effect without any additional tools:
diff --old-group-format=$'\e[0;31m%<\e[0m' \
--new-group-format=$'\e[0;...
- 74k
28
votes
What does //1/ mean
For the most part, multiple slashes are equivalent to a single slash. There's one exception: paths beginning with exactly two slashes (//foo/…, as opposed to /foo/… or ///foo/…) have a different ...
23
votes
Find directories that do not contain subdirectories
If you are able to use find and if you are working on a "normal Unix filesystem" (that is, as defined in find(1) under -noleaf option description), then the following command can be used:
find . -...
- 5,041
23
votes
Delete First line of a file
This topic is interest, so I test the benchmark in 3 ways:
sed '1d' d.txt > tmp.txt
tail -n +2 d.txt > tmp.txt
sed -i '1d' d.txt
Note that target d.txt is 5.4GB file
Get the result :
run 1 ...
- 331
23
votes
Accepted
Is the shell ksh93 dead?
NO
tldr: github.com/att/ast and github.com/att/uwin
On Jan 19-20, 2016 the following (1|2) messages were posted to the ast-users mailing-list: (and I consider the dgk has some patches comment ...
- 57.2k
23
votes
Accepted
How to use associative arrays safely inside arithmetic expressions?
The problem is that in a shell arithmetic expression, such as inside $((...)) (POSIX), or ((...)) (ksh/bash/zsh), or array indices or arguments of some shell builtins or [[...]] operands, word ...
- 513k
21
votes
Accepted
exit trap in dash vs ksh and bash
zsh, pdksh (though not recent versions of mksh derived from that), yash, the Bourne shell behave like dash.
Only bash, ksh88, ksh93 and mksh behave otherwise.
The POSIX spec is not clear on what ...
- 513k
19
votes
Accepted
Equivalent to "source" in OpenBSD?
You are using the Forsyth PD Korn shell, the usual login shell on OpenBSD. The PD Korn shell does not have a source command. The source built-in command is only available in some shells. The ...
- 66k
17
votes
Accepted
KSH/BASH Maximum size of an Array
i=0
while true; do
a[$i]=foo
i=$((i+1))
printf "\r%d " $i
done
This simple script shows on my systems (Gnu/Linux and Solaris):
ksh88 limits the size to 2^12-1 (4095). (subscript out of ...
- 60k
16
votes
telnet command with custom timeout duration
This will run for no more than 2 secounds:
[]# echo quit | timeout --signal=9 2 telnet [SERVER] [PORT]
- 169
16
votes
Preferred syntax for two lines long pipe
I'm going to disagree with most folks here; I always prefer to wrap before a joining operator such as a pipe:
command1 \
| command 2
(You don't need to indent the second line; the pipe itself links ...
- 261
14
votes
Accepted
What does "set -f" in Korn Shell do?
set -f is the portable (i.e. POSIX) way to disable filename expansion.
When enabled (by default or with set +f), filename expansion is an operation performed by the shell that replaces, when possible,...
- 60k
13
votes
Why does parameter expansion with spaces without quotes work inside double brackets "[[" but not inside single brackets "["?
When should I assign double quotes around variables like "${var}" to prevent problems caused by spaces?
Implicit in this question is
Why isn’t ${variable_name} good enough?
${...
13
votes
How to use and/or conditional in shell script
The standard (POSIX sh and utilities) canonical legible ways would be:
string comparison:
if [ "$a" != 0 ] || [ "$b" != 100 ]; then...
decimal integer comparison (0100 is 100, whether leading ...
- 513k
13
votes
Is the shell ksh93 dead?
Yes and no. The official AT&T Korn Shell may be pining for the fjords, but there are two actively developed clones.
There's pdksh, the public domain clone of the Korn shell, but that hasn't been ...
- 361
13
votes
Accepted
How to subtract two list (fast)?
You can use comm to remove anything that’s common to both lists:
listr=($(comm -3 <(printf "%s\n" "${list1[@]}" | sort) <(printf "%s\n" "${list2[@]}" | sort) | sort -n))
This sorts both lists ...
- 402k
13
votes
Are Here-Strings available in ksh88?
No, here strings are not available on ksh88 and pdksh. On the more recent ksh93 (original AT&T Korn Shell) and mksh (currently actively developed pdksh derivative) it is, however, available.
<&...
- 1,715
13
votes
How to put a string search with grep command into if statement?
Another option:
grep -qw -- "$users" "$file1"; in_file1=$?
grep -qw -- "$users" "$file2"; in_file2=$?
case "${in_file1},${in_file2}" in
0,0) echo found in both files ;;
0,*) echo only in ...
- 83.2k
12
votes
How to color diff output?
Try colordiff file1 file2
Availability of colordiff with your Linux/BSD distribution
Those running Debian or Ubuntu (or any of their derivatives) can probably
just use "apt-get install colordiff&...
- 231
12
votes
check if date argument is in yyyy-mm-dd format
This will check for the correct format (YYYY-MM-DD) in bash (with built-in regex match):
if [[ $1 =~ ^[0-9]{4}-[0-9]{2}-[0-9]{2}$ ]]
then echo "Date $1 is in valid format (YYYY-MM-DD)"
else echo "...
- 1,406
Only top scored, non community-wiki answers of a minimum length are eligible