linux shell ----test commond or [expr]

test command or [ expr ] is used to see if an expression is true, and if it is true it return zero(0), otherwise returns nonzero for false

Syntax: 
test expression OR [ expression ]

eg.

# Script to see whether argument is positive
#
if test $1 -gt 0
then
echo "$1 number is positive"
fi

测试给shell传递的第一个参数的判断，主要是掌握test的用法。

test or [ expr ] works with
1.Integer ( Number without decimal point)
2.File types
3.Character strings

For Mathematics, use following operator in Shell Script

Mathematical Operator in  Shell Script MeaningNormal Arithmetical/ Mathematical StatementsBut in Shell   For test statement with if commandFor [ expr ] statement with if command-eqis equal to5 == 6if test 5 -eq 6if [ 5 -eq 6 ]-neis not equal to5 != 6if test 5 -ne 6if [ 5 -ne 6 ]-ltis less than5 < 6if test 5 -lt 6if [ 5 -lt 6 ]-leis less than or equal to5 <= 6if test 5 -le 6if [ 5 -le 6 ]-gtis greater than5 > 6if test 5 -gt 6if [ 5 -gt 6 ]-geis greater than or equal to5 >= 6if test 5 -ge 6if [ 5 -ge 6 ]

OperatorMeaningstring1 = string2string1 is equal to string2string1 != string2string1 is NOT equal to string2string1string1 is NOT NULL or not defined -n string1string1 is NOT NULL and does exist-z string1string1 is NULL and does exist

TestMeaning-s file   Non empty file-f file   Is File exist or normal file and not a directory -d dir    Is Directory exist and not a file-w file  Is writeable file-r file   Is read-only file-x file   Is file is executable