Shell编程——弱数据类型的脚本语言快速入门指南

hann@HannYang:~$ help -m if
NAME
    if - Execute commands based on conditional.
SYNOPSIS
    if COMMANDS; then COMMANDS; [ elif COMMANDS; then COMMANDS; ]... [ else COMMANDS; ] fi
DESCRIPTION
    Execute commands based on conditional.
    The `if COMMANDS' list is executed.  If its exit status is zero, then the
    `then COMMANDS' list is executed.  Otherwise, each `elif COMMANDS' list is
    executed in turn, and if its exit status is zero, the corresponding
    `then COMMANDS' list is executed and the if command completes.  Otherwise,
    the `else COMMANDS' list is executed, if present.  The exit status of the
    entire construct is the exit status of the last command executed, or zero
    if no condition tested true.
    Exit Status:
    Returns the status of the last command executed.
......

hann@HannYang:~$ help -m case
NAME
    case - Execute commands based on pattern matching.
SYNOPSIS
    case WORD in [PATTERN [| PATTERN]...) COMMANDS ;;]... esac
DESCRIPTION
    Execute commands based on pattern matching.
    Selectively execute COMMANDS based upon WORD matching PATTERN.  The
    `|' is used to separate multiple patterns.
    Exit Status:
    Returns the status of the last command executed.
......

hann@HannYang:~$ help -m for
NAME
    for - Execute commands for each member in a list.
SYNOPSIS
    for NAME [in WORDS ... ] ; do COMMANDS; done
DESCRIPTION
    Execute commands for each member in a list.
    The `for' loop executes a sequence of commands for each member in a
    list of items.  If `in WORDS ...;' is not present, then `in "$@"' is
    assumed.  For each element in WORDS, NAME is set to that element, and
    the COMMANDS are executed.
    Exit Status:
    Returns the status of the last command executed.
......

hann@HannYang:~$ help -m while
NAME
    while - Execute commands as long as a test succeeds.
SYNOPSIS
    while COMMANDS; do COMMANDS; done
DESCRIPTION
    Execute commands as long as a test succeeds.
    Expand and execute COMMANDS as long as the final command in the
    `while' COMMANDS has an exit status of zero.
    Exit Status:
    Returns the status of the last command executed.
......

hann@HannYang:~$ help -m until
NAME
    until - Execute commands as long as a test does not succeed.
SYNOPSIS
    until COMMANDS; do COMMANDS; done
DESCRIPTION
    Execute commands as long as a test does not succeed.
    Expand and execute COMMANDS as long as the final command in the
    `until' COMMANDS has an exit status which is not zero.
    Exit Status:
    Returns the status of the last command executed.
......

hann@HannYang:~$ help -m break
NAME
    break - Exit for, while, or until loops.
SYNOPSIS
    break [n]
DESCRIPTION
    Exit for, while, or until loops.
    Exit a FOR, WHILE or UNTIL loop.  If N is specified, break N enclosing
    loops.
    Exit Status:
    The exit status is 0 unless N is not greater than or equal to 1.
......

hann@HannYang:~$ help -m continue
NAME
    continue - Resume for, while, or until loops.
SYNOPSIS
    continue [n]
DESCRIPTION
    Resume for, while, or until loops.
    Resumes the next iteration of the enclosing FOR, WHILE or UNTIL loop.
    If N is specified, resumes the Nth enclosing loop.
    Exit Status:
    The exit status is 0 unless N is not greater than or equal to 1.
......

hann@HannYang:~$ help -m function
NAME
    function - Define shell function.
SYNOPSIS
    function name { COMMANDS ; } or name () { COMMANDS ; }
DESCRIPTION
    Define shell function.
    Create a shell function named NAME.  When invoked as a simple command,
    NAME runs COMMANDs in the calling shell's context.  When NAME is invoked,
    the arguments are passed to the function as $1...$n, and the function's
    name is in $FUNCNAME.
    Exit Status:
    Returns success unless NAME is readonly.

hann@HannYang:~$ function add {
>     num1=$1
>     num2=$2
>     sum=$((num1 + num2))
>     echo "The sum of $num1 and $num2 is $sum."
> }
hann@HannYang:~$ add 10 20
The sum of 10 and 20 is 30.

hann@HannYang:~$ function sub { num1=$1; num2=$2; sum=$((num1 - num2)); echo "The difference between $num1 and $num2 is $sum."; }
hann@HannYang:~$ sub 30 20
The difference between 30 and 20 is 10.

hann@HannYang:~$ factorial() {
>     if [ $1 -le 1 ]
>     then
>         echo 1
>     else
>         echo $(( $1 * $(factorial $(( $1 - 1 ))) ))
i
}>     fi
> }
hann@HannYang:~$ read -p "请输入一个整数：" num
请输入一个整数：6
hann@HannYang:~$ result=$(factorial $num)
hann@HannYang:~$ echo "$num 的阶乘为 $result"
6 的阶乘为 720

hann@HannYang:~$ for i in 1 2 3 4 5; do echo -n $i; done; echo
12345
hann@HannYang:~$ for i in {1..5}; do echo -n $i; done; echo
12345
hann@HannYang:~$ sum=0;for i in {1..100};do let sum+=i;done;echo $sum
5050
hann@HannYang:~$ for i in {1..5}{8..10}; do echo -n $i; done; echo
18191102829210383931048494105859510
hann@HannYang:~$ for i in {1..5}{8..10}; do echo -n $i" "; done; echo
18 19 110 28 29 210 38 39 310 48 49 410 58 59 510
hann@HannYang:~$ for i in {A..C}{a..d}; do echo -n $i" "; done; echo
Aa Ab Ac Ad Ba Bb Bc Bd Ca Cb Cc Cd

#!/bin/bash
for i in {1..9}
do
   for j in {1..9}
   do
     if [ $j -le $i ]
     then
        echo -n "$j*$i=$(($i*$j)) "
     fi
   done
   echo ""
done

#!/bin/bash
for i in {1..9}
do
   for j in {1..9}
   do
     if [ $j -le $i ]
     then
        printf "%d*%d=%2d " $j $i $(($i*$j))
     fi
   done
   echo ""
done

#!/bin/bash
for i in {1..9}
do
   for j in {1..9}
   do
     if [ $j -le $i ]
     then
        if [ $j -eq 1 ]
        then
            printf "%d*%d=%d " $j $i $(($i*$j))
        else
            printf "%d*%d=%2d " $j $i $(($i*$j))
        fi
     fi
   done
   echo ""
done