String operations in bash Script Programming

One of the string operations: test the existence of Variables

$ {Varname:-word}	If varname exists and is not null, return its value; otherwise, return word
$ {Varname: = word}	If varname exists and is not null, return its value. Otherwise, set it to word and return its value.
$ {Varname :? Message}	If varname exists and is not null, return its value. Otherwise, print varname: followed by message and exit the current command or script.
$ {Varname: + word}	If varname exists and is not null, word is returned; otherwise, null is returned.
$ {Varname: Offset}	Offset characters, take all remaining characters
$ {Varname: offset: length}	Offset characters, length characters

# Echo $ {age:-30} // If the variable Age is not set, 3030 # age = 28 # echo $ {age:-30} is returned. // If the variable age is set to 28, 2828 # name = King # echo $ {Name: = Tom} is returned. // If the variable name is set to King, kingking # unset name # echo $ {Name: = Tom} // The variable name is cleared. If not set, set the variable name to tomtom # echo $ nametom # echo $ {sex :? "What's your sex? "}-Bash: Sex: What's your sex? // The variable sex is not set to show what's your sex? # Sex = female # echo $ {sex :? "What's your sex? "} // The variable sex has been set. femalefemale # echo $ {ID: +" not null "} // The variable ID is not set, returns NULL # id = 100 # echo $ {ID: + "not null"} // The variable ID has been set. The returned message is not nullnot null # echo $ {MSG: 5} // offset of 5 characters, take all remaining characters world # echo $ {MSG: 5: 2} // offset of 5 characters, take two characters wo

String operation 2: calculate the number of characters in the Variable

$ {# Varname}

# echo $msgHelloWorld# echo ${#msg} 10

String operation 3: Use mode and mode matching to operate the string

$ {Varname # pattern}	If the pattern matches the beginning of the variable value, delete the shortest matching part and return the remaining part.
$ {Varname ## pattern}	If the pattern matches the beginning of the variable value, delete the longest matching part and return the remaining part.
$ {Varname % pattern}	If the pattern matches the end of the variable value, delete the shortest matching part and return the remaining part.
$ {Varname % pattern}	If the pattern matches the end of the variable value, delete the longest matching part and return the remaining part.
$ {Varname/pattern/string}	Replace the first part that matches pattern with string
$ {Varname // pattern/string}	Replace all matching parts of pattern with string

# Var=/etc/sysconfig/network-scripts/ifcfg-eth0      # echo $Var/etc/sysconfig/network-scripts/ifcfg-eth0# echo ${Var#/*/}sysconfig/network-scripts/ifcfg-eth0# echo ${Var##/*/}ifcfg-eth0# Var=/home/yy/test.conf.bak# echo $Var/home/yy/test.conf.bak# echo ${Var%.*}/home/yy/test.conf# echo ${Var%%.*}/home/yy/test# echo $msgHelloWorld# echo ${msg/o/O}  HellOWorld# echo ${msg//o/O} HellOWOrld

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String operations in bash Script Programming