Bash has a powerful parameter syntax. The examples below show a command on the left, the result (if
any) in the center, and an explanation on the right. See “Parameter Expansion” in the bash man page.
Set Up the Test Directory
Код:
mkdir test
cd test
touch file1 file2 file3
Basic Parameter Expansion
Код:
param1=hello
echo $param1 hello
echo ${param1}a helloa the braces separate the name
echo ${param2} nothing there Default Values
Код:
echo ${param2:-file*} file1 file2 file3 all files in the directory
echo ${param2:-$param1} hello uses $param1's value...
echo $param2 (nothing) ... but didn't change $param2
echo ${param3:=$param1} hello uses $param1's value...
echo $param3 hello ... and assigns it to $param3 Substring Manipulations
Keep in mind that the substitutions etc are expanded, not literals, so you can use wildcards and other
pattern syntaxes in them (for example, the “he*l” below used to strip “hell” from the value).
Код:
echo ${param1:2} llo substring from 2
echo ${param1:2:2} ll substring from 2, len 2
echo ${param1#he} llo strip shortest match from start
echo ${param1#hel*} lo strip shortest match from start
echo ${param1#he*l} lo strip shortest match from start
echo ${param1##he*l} o strip longest match from start
echo ${param1%l*o} hel strip shortest match from end
echo ${param1%%l*o} he strip longest match from end
echo ${param1/l/p} heplo replace as few as possible
echo ${param1//l/p} heppo replace as many as possible Miscellaneous
Код:
echo ${!param*} param1 param2 param3 parameter names starting with...
echo ${#param1} 5 length of parameter value Example Uses
# Rename all .GIF files to .gif
Код:
for file in *.GIF; do mv $file ${file%GIF}gif; done # Now number the files sequentially
Код:
cnt=0;
for file in *.gif; do mv $file $cnt$file; let cnt=cnt++; done
# Oops, I didn't mean that... get rid of the numbers.
Код:
for file in *.gif; do mv $file ${file##[0-9]}; done