5. Korn Shell Built in Comparison operators
| Use [[ ]] to compare string values | Use (( )) to compare numerical values |
| i.e. string equality, lexical order, length and comparison with a pattern | i.e. numerical relational operators, equality, inequality. no $ needed within (( )) |
6. NOTE: The result or status of any Unix command is given by:
0 means successful
non-zero means unsuccessful
Show the result via: $ print $? immediately after the unix command
BUT: The result of the command: (( n )) is given as successful
if n is non-zero
unsuccessful if n is 0
Show the result via: $ (( n ))
$ print $? $n
7. test (and [ ] ) Comparison operators for numbers (Bourne and Korn Shell)
| Symbol | Meaning |
| -eq | equal |
| -ne | not equal |
| -gt | greater than |
| -lt | less than |
| -ge | greater or equal |
| -le |
less than or equal |
| ! | not |
| -a | Boolean AND |
| -o | Boolean inclusive OR |
| -z string | true if string length = 0 |
| -n string | true if string length > 0 |
| string1 = string2 | true if strings are the same |
| string1 != string2 | true if strings are not equal |
| string | true if string not the null string |
8. Example using test and [ ] $ x=4 $ y=6 $ test $x -gt $y # same as $ [ $x -gt $y ] $ print $? 1 $ test $x -lt $y # same as $ [ $x -lt $y ] $ print $? 0 9. Korn Shell String Comparison Syntax Summary
| Comparison | Meaning |
| [[ string1 = string2 ]] | string1 is identical to string2 |
| [[ string1 = pattern ]] | string1 matches (shell) pattern |
| [[ string1 != string2 ]] | string1 is not identical to string2 |
| [[ string1 != pattern ]] | string1 does not match (shell) pattern |
| [[ string1 < string2 ]] | string1 precedes string2 in lexical order |
| [[ string1 > string2 ]] | string1 follows string2 in lexical order |
| [[ -z string ]] | string's length is 0 ( string is the null string) |
| [[ -n string ]] | string's length is non-zero |
10. Korn Shell Arithmetic Operators These operators can be used by the built-in let command and by (( )). Their precedence order is from highest to lowest.
| Operator Symbol | Meaning | Example |
| (...) | Grouping To override precedence order | $ (( a=(7+5) * (5-3) )) $ print $a 24 |
| - | unary minus | $ negative=-1 $ print -- $negative -1 |
| ! | Logical negation | $ a=1 $ (( b = ! a )) $ print $a $b 1 0 |
| ~ | Bitwise negation | $ a=2#1011 $ typeset -i2 c $ (( c = ~ a )) $ print $a $c 2#1011 -2#1100 |
| * / % | Multiplication; Division; Remainder | $ (( y = 5 * 8 )) $ (( x = 37 / 5 )) $ (( z = 37 % 5 )) $ print $y $x $z 40 7 2 |
| + - | Addition; Subtraction | $ (( r = x + z )) $ (( s = x - z )) $ print $r $s 9 5 |
| << >> | Left Shift; Right Shift | $ (( y = 2#1101 << 2 )) $ (( z = 2#1011 >> 2 )) print $y $z 52 2 |
| <= >= < > == != | Comparison Operators | $ print $(( y > z )) 1 $ print $(( y < z )) 0 |
| & | Bitwise AND | $ typeset -i2 n $ (( n = w = 2#1010 & 2#1100 )) $ print $w $n 8 2#1000 |
| ^ | Bitwise Exclusive OR (XOR) | $ typeset -i2 m $ (( m = v = 2#1010 ^ 2#1100 )) $ print $v $m 6 2#110 |
| | | Bitwise Inclusive OR | $ typeset -i2 t $ (( u = 2#1010 | 2#1100 )) $ t=$u $ print $u $t 14 2#1110 |
| && | Logical AND | $ a=7 b=-5 c=0 $ print $(( a && b)) $(( a && c )) 1 0 |
| || | Logical (Inclusive) OR | $ a=7 b=-5 c=0 $ print $(( a || b)) $(( a || c )) $(( c || c )) 1 1 0 |
| = | Assignment | $ a=b=c=7 $ print $a $b $c 7 7 7 |
| *= /= %= | Compound Arithmetic | $ typeset -i2 b $ a=36 $ (( b = (a /= 12) )) $ print $ a $b 3 2#11 |
| += -= <<= >>= | Compound Arithmetic; Compound Shift | $ typeset -i2 b $ a=36 $ (( b = ( a >>= 3 ) )) $ print $a $b 4 2#100 |
| &= ^= |= | Compound Bitwise AND, XOR, OR | $ typeset -i2 w=2#1010 $ ((n = (w &= 2#1100 ) )) $ print $w $n 8 2#1000 |
11. Korn Shell File Object Comparisons
| Bourne Shell test? |
File Object Comparison | Returns true ( Successful) if object: |
| [[ -a object ]] | exists; any file type is ok | |
| yes | [[ -f object ]] | is a regular file (or symbolic link!) |
| yes | [[ -d object ]] | is a directory |
| [[ -c object ]] | is a character special file | |
| [[ -b object ]] | is a block special file | |
| [[ -p object ]] | is a named pipe file | |
| [[ -S object ]] | is a socket file | |
| [[ -L object ]] | is a symbolic (Soft) link | |
| yes | [[ -s object ]] | is not empty; number of bytes greater than 0 |
| yes | [[ -r object ]] | is readable |
| yes | [[ -w object ]] | is writeable or modifiable |
| yes | [[ -x object ]] | is executable or searchable (directory) |
| [[ -u object ]] | has setuid bit set | |
| [[ -g object ]] | has setgid bit set | |
| [[ -k object ]] | has sticky bit set | |
| [[ -O object ]] | is owned by the user | |
| [[ -G object ]] | is in the group owned by the user | |
| [[ object1-nt object2 ]] | object1 is newer than object2 | |
| [[ object1-ot object2 ]] | object1 is older than object2 | |
| [[ object1-ef object2 ]] | object1 is effectively another name for object2 |