Shell basic syntax --- common conditional

grammar

　　[Analyzing Expression]

 

Folder or path exists

• -e target is present (exist)
• -d whether the path (directory)
• Whether -f file (file)

[-E text. SH ] || Touch text. SH   # text.sh does not exist to create

 

The existence of rights

• Are -r has read access (read)
• Whether -w have write access (write)
• Are -x Executive authority (excute)

[Named text.txt in the -X-] && echo  ' Executive authority '    # determines whether permission to execute

 

Integer comparison size (only for comparison integer)

• -eq equal (equal)

• -ne not equal (not equal)

• -gt greater than (greater than)

• -lt less than (lesser than)

• -ge greater than or equal to (greater or equal)

• -le less than or equal to (lesser or equal)

[ . 9 -gt . 8 ] && echo  ' greater than '

 

Compare the size of the float (With bc)

• Comparison of the size bc, true: 1 false: 0

` Echo  ' 1.2 <1.3 ' | bc` # bc size comparison using 
[` echo  ' 1.2 <1.3 ' | bc` -eq 1 ] # 1 and then compared. The results can be derived

 

String comparison

• Equal =

• = Equivalent to == Equal to different only in [[]] and the performance in []

• ! = Not equal

[ ' Kkkkk ' ! = ' Kkkk ' ] && echo  ' not equal '

 

Multi-conditional

# [[]] && and || only with the use of 
[[ " A " = " A " && " B " = " B " ]] 

# [] which can only fit -a -o or use, with the outside to && || or using 
[ " A " = " A " -a " B " = " B " ] 

[ " A " = " A " -o " B " = "b" ]

[ "a" = "a"] && [ "b" = "b" ]