String processing-$ {#}, expr length, expr index, expr match, extract substrings

{#}, Expr length "$ Str" [[email protected] shell] # STR = "My name is mah" [[email protected] shell] # echo $ {# STR} 14 [[email protected] shell] # expr length $ strexpr: syntax error [[email protected] shell] # expr length "$ Str" # Double quotation marks must be added to 14 ####### expr Index "$ Str" Mah [[email protected] shell] # STR = "My name is mah" [[email protected] shell] # expr Index "$ Str" mah12 [[email protected] shell] # expr Index "$ str "O # No, returns 00 [[email protected] shell] # expr Index "$ Str" ay # Although ay exists, however, the returned result is Y location 2 [[email protected] shell] # expr Index "$ Str" an4

###### Expr match $ string $ substring

Matches the substring string at the beginning of string and returns the length of the matched string.

[[Email protected] shell] # STR = "My name is mah" [[email protected] shell] # expr match "$ Str" My * 2 [[email protected] shell] # expr match "$ Str" Mah # although the string contains Mah, however, mah does not start with 0 [[email protected] shell] # expr match "$ Str" M * 1 [[email protected] shell] # expr match "$ Str" M. * # regular expression. * Indicates all 14

#### $ {STR: Position: length} string pruning, two Methods: [email protected] shell] # STR = "ABC def Ghi" [[email protected] shell] # echo $ {STR: 0} ABC def Ghi [[email protected] shell] # echo $ {STR: 0: 3} #0 indicates the first digit, 3 represents the length ABC [[email protected] shell] # echo $ {STR: 0: 5} ABC d [[email protected] shell] # echo $ {STR: -3} #-There is no space at the front, show all strings ABC def ghiyou have new mail in/var/spool/mail/root [[email protected] shell] # echo $ strabc def Ghi [[email protected] shell] # echo $ {STR: -3 }#-trim the Ghi [[email protected] shell] # echo $ {STR: -6} EF Ghi [[email protected] shell] # expr substr "$ Str" 1 3 # expr substr "$ Str" format. The first digit is the 1st digit, there must be two parameters: ABC [[email protected] shell] # expr substr "$ Str" 1 5abc d

###### Use a regular expression when processing a string. Note: There must be spaces on both sides of the colon; otherwise, the syntax is incorrect.

Substring starting with a string: Two Methods

[[Email protected] shell] # STR = "012345 my name is mah" [[email protected] shell] # expr match "$ Str" '\ ([0-9] * \) '# Method 1: Use match012345 [[email protected] shell] # expr "$ Str":' \ ([0-9] * \) '# Method 2: Use the colon 012345

Cut the substring at the end of the string: the difference is that \ (add before .*

[[Email protected] shell] # echo $ str012345 my name is mah [[[email protected] shell] # expr match "$ Str "'. *\(... \)'#. it indicates a character mah [[email protected] shell] # expr "$ Str ":'. *\(... \) 'mah

###### Delete a substring: Format: $ {}

Category 1: delete from the beginning

[[Email protected] shell] # echo $ str012345 my name is mah [[[email protected] shell] # echo $ {STR #0123} 45 my name is mah [[email protected] shell] # echo $ {STR #345} 012345 my name is mah [[email protected] shell] # echo $ {STR #0*5} # Here * is not a regular expression, it only indicates all characters from 0 to 5, my name is mah [[[email protected] shell] # echo $ {STR #0*5 }## greedy mode my name is mah

Category 2: deleting from the end

[[Email protected] shell] # echo $ {STR % mah} 012345 my name is [[email protected] shell] # echo $ {STR % m * h} 012345 [[ email protected] shell] # echo $ {STR % m. * h} # It can be seen that * is not a regular expression 012345 my name is mah

####### Replace a string

[[Email protected] shell] # STR = "0011 my name is mah 0011" [[email protected] shell] # echo $ {str/0*1/YYY} YYY [[ email protected] shell] # echo ${str/0 **/YYY} YYY [[[email protected] shell] # echo $ {str/0*0/YYY} # * not a regular expression, however, it indicates all the characters yyy11 [[[email protected] shell] # echo $ {STR // 0*0/YYY} yyy11 [[email protected] shell] # echo ${str/0 * m/YYY} yyyah 0011 another two special replacements #1. replace [[email protected] shell] # echo $ {str/#0011/MAH} mah my name is mah 0011 #2. replace [[email protected] shell] # echo $ {STR} 0011 my name is mah 0011 [[email protected] shell] # echo $ {str/% 0011/MAH} 0011 my name is mah 0011 [[email protected] shell] # STR = "123 my name is mah" [[email protected] shell] # echo $ {str/% m * H /MAH} 123 MAH

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