Examples of string manipulation and for loop statements in shell
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The code is as follows:
#! / bin/bash
My_name= "jxq"
Echo $my_name
Echo ${my_name}
#--
# string operation
#--
# restrictions on single quotation mark strings, but not on double quotation marks:
# any character in the single quote will be output as is, and the variable in the single quote string is invalid
# single quotation marks cannot appear in single quotation marks (not even after using escape characters for single quotation marks)
Name= "will"
Age=24
My_full_name='$ {name} ${age}'
Echo ${my_full_name}
My_full_name= "${name} ${age}"
Echo ${my_full_name}
# string concatenation
Echo ${name} ${age}
# string length
Echo ${# name} # 4
# substring
Message= "I want to be healthy"
Echo ${message:2} # want to be health, 2 is position
Echo ${message:2:4} # want,2 is position,4 is len
# delete shortest match from front: ${string#substring}
Echo ${message#*want}
# delete shortest match from back: ${string%substring}
Echo ${message%healthy}
# delete longest match from front: ${string##substring}
Echo ${message##*h}
# delete longest match from back: ${string%%substring}
Echo ${message%%t*}
# find and replace: ${string/pattern/replacement}
Book_name= "Catch Eye Eye"
Echo ${book_name/Eye/Cat}
# find and replace all match: ${string//pattern/replacement}
Echo ${book_name//Eye/Cat}
File_path= "/ usr/local/bin"
# only replace when pattern match the beginning: ${string/#pattern/replacement}
Echo ${file_path/#\ / usr/tmp}
# only replace when pattern match the end: ${string/%pattern/replacement}
Echo ${file_path/%bin/tmp}
# string index
StringZ=abcABC123ABCabc
Echo `expr index "$stringZ" C12` # Mac OSX does not support expr
#--
# statement
#--
# if
If true
Then
Echo "ok, true"
Fi
# write on one line
If true; then echo "ok"; fi
Var='12'
If [$var-eq 12]; then
Echo "This is a numeric comparison if example"
Fi
If ["$var" = "12"]; then
Echo "This is a string if comparison example"
Fi
If [["$var" = * 12*]]; then
Echo "This is a string regular expression if comparison example"
Fi
Name= "jxq"
If ["$name" = "jxq"]; then
Echo "hello" $name
Fi
# Loop statement
For item in `ls * .sh`
Do
Echo $item
Echo "completed"
Done
# write on one line
For item in `ls * .sh`; do echo $item; echo "completed"; done
Counter=1
While:
Do
Echo "bee"
Let "counter=$counter+1"
If [$counter-eq 3]; then
Break # break/continue is similar to Java
Fi
Done
# Case statement
Opt= "install"
Case "${opt}" in
"install")
Echo "install..."
Exit
"update")
Echo "update..."
Exit
*) echo "bad opt"
Esac
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