Linux Shell 03 Process Control statements

I. If statement format: Supports if/elif/else forms, supports nesting

1. When command execution succeeds (and exit status is 0), execute Command2

2. When the judging condition is the test command, the Command2 is executed when the result is true

if command; then   Command1
Else
Command2fiif commandthen    commandfi

Two. For statement format

 for var inch List  Do     Commanddone

1. Read the list of values

A. The values in the list are separated by a space by default,

B. Include single quotes in the value to escape or use double quotation marks

C. The value contains spaces, which need to be enclosed in double quotation marks.

 for var inch I\'m come from Nanjing and I want go to "New York", I can\ ' t say Francedo    echo $
   
    var
     Done
   

2. Reading a list from a variable

list="AAA BBB CCC"list= $list"  CCC"    #字符串追加内容  for var inch List  Do     echo $var Done

3. Read the command value

 for var  in ' cat/etc/passwd 'does    echo $var Done

4. Field Separators

In the 3 example, the content is not output on a row, because space/tab/line breaks are considered field separators in the shell

In the example above, if you want content to be output by row, you need to modify the field delimiter

Ifs. old=$IFSIFS=$'\ n'forvar in ' cat/etc/passwd '  do    echo $vardoneifs= $IFS. Old

Three. While statement

Four. Do...until statements

Five. Continue and break statements

Linux Shell 03 Process Control statements