Difference between revisions of "Bash:Variables"
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− | [[Category: | + | [[Category:Linux/Unix]] |
=Arithmetics= | =Arithmetics= | ||
Line 18: | Line 18: | ||
:Calculate and assign to VAR | :Calculate and assign to VAR | ||
;let VAR+=2 | ;let VAR+=2 | ||
+ | ;VAR=$((VAR += 2)) | ||
:Add two to VAR | :Add two to VAR | ||
Line 37: | Line 38: | ||
;$! | ;$! | ||
:ProcessID of last spawned process. | :ProcessID of last spawned process. | ||
+ | |||
+ | =Nested variables= | ||
+ | ;var2=${!var1} | ||
+ | :var2 will get the value of the evaluation of var1 (value of var0) | ||
+ | <syntaxhighlight lang=bash> | ||
+ | var0=1 | ||
+ | var1=var0 | ||
+ | var2=${!var1} | ||
+ | echo $var2 | ||
+ | 1 | ||
+ | </syntaxhighlight> | ||
=Loop over a range= | =Loop over a range= | ||
Line 49: | Line 61: | ||
echo $i | echo $i | ||
done | done | ||
+ | </syntaxhighlight> | ||
+ | |||
+ | =Operations on variables= | ||
+ | * # searches from the beginning | ||
+ | * % searches from the end | ||
+ | |||
+ | ;${var#??} | ||
+ | :Remove the first 2 chars | ||
+ | ;${var%??} | ||
+ | :Remove the last 2 chars | ||
+ | ;${var%e*} | ||
+ | :Remove everything from and including the last 'e' | ||
+ | ;${var#*e} | ||
+ | :Remove everything up to the first 'e' | ||
+ | ;${var#* * } | ||
+ | :Remove the first 2 words from a line (carefully check the spaces) | ||
+ | ;${var% * *} | ||
+ | :Remove the last 2 words from a line (carefully check the spaces) | ||
+ | ;${#var} | ||
+ | :Length of the string | ||
+ | |||
+ | ;Check if a string is in the variable | ||
+ | The trick is that if the variable does not have the searchstring the variable will be unchanged. | ||
+ | <syntaxhighlight lang=bash> | ||
+ | if [ "${var#*searchstring}" != "${var}" ] | ||
+ | then | ||
+ | echo "searchstring is in $var" | ||
+ | fi | ||
</syntaxhighlight> | </syntaxhighlight> |
Latest revision as of 20:49, 11 April 2022
Arithmetics
Bash and ksh only work with integers.
- +, -, *, /, %
- add, substract, multiply, divide, modulo.
- **
- For bash, Exponentiation
- 10#00012
- For bash, force the figure (00012) to be interpreted as decimal. Figures starting with 0 are considered octal by default.
- expr <expr>
- Voer expr uit, bij boolean wordt 1 (onwaar) of 0 (waar) gegeven
- ((VAR=x+y))
- let VAR=x+y
- VAR=$((x+y))
- VAR=$(expr x + y)
- Calculate and assign to VAR
- let VAR+=2
- VAR=$((VAR += 2))
- Add two to VAR
Special Parameters
- $0
- Name current procedure
- $1
- First passed argument ($2 is the second, $3... )
- $*
- All arguments given as one string
- $@
- All arguments given as separate strings per parameter
- $#
- The number of passed arguments
- $?
- The returnstate for the last executed command. 0 = OK, all others not.
- $$
- ProcessID of current process, handy to use for temporary files
- $!
- ProcessID of last spawned process.
Nested variables
- var2=${!var1}
- var2 will get the value of the evaluation of var1 (value of var0)
var0=1
var1=var0
var2=${!var1}
echo $var2
1
Loop over a range
for i in {00..59}
do
echo ${i}
done
for i in $(seq ${START} ${END})
do
echo $i
done
Operations on variables
- # searches from the beginning
- % searches from the end
- ${var#??}
- Remove the first 2 chars
- ${var%??}
- Remove the last 2 chars
- ${var%e*}
- Remove everything from and including the last 'e'
- ${var#*e}
- Remove everything up to the first 'e'
- ${var#* * }
- Remove the first 2 words from a line (carefully check the spaces)
- ${var% * *}
- Remove the last 2 words from a line (carefully check the spaces)
- ${#var}
- Length of the string
- Check if a string is in the variable
The trick is that if the variable does not have the searchstring the variable will be unchanged.
if [ "${var#*searchstring}" != "${var}" ]
then
echo "searchstring is in $var"
fi