[Linux 文章收集] Bash - How to trim string

Source From Here
How-To
You can use a bash parameter expansion, sed, cut and tr to trim a string.

Bash parameter expansion
Let's use bash parameter expansion to remove all whitespace characters from the variable foo:
- test1.sh

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1. #!/bin/sh  
2. foo="Hello    world."  
3. echo "${foo//[[:space:]]/}"  

Execution result:

# ./test1.sh
Helloworld.

Using sed command to trim the front/back space
To remove only space characters before and after string use sed:
- test2.sh

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1. #!/bin/sh  
2. foo="      Hello    world.    "  
3. echo "${foo}" | sed -e 's/^[[:space:]]*//'  

Execution result:

# ./test2.sh
Hello world.

Using xargs to remove space
Easy to use and remember way how to remove whitespaces before and after word:
- test3.sh

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1. #!/bin/sh  
2. foo="      Hello    world.    "  
3. foo_remove_space=`echo ${foo} | xargs`  
4. echo "foo_remove_space='${foo_remove_space}'"  

Execution result:

# ./test3.sh
foo_remove_space='Hello world.'

Supplement
* Split string by delimiter and get N-th element
* Linux 系統 xargs 指令範例與教學