shell 语法与C语言对比

要实现的功能	C语言编程	Linux Shell脚本编程
程序/脚本的参数传递	int main(int argc, char** argv) { if (argv != 4) {     printf( “Usage: %s arg1 arg2 arg3”, argv[0] );     return 1; }   printf(“arg1:%s/n”,argv[1]); printf(“arg2:%s/n”,argv[2]); printf(“arg3:%s/n”,argv[3]); return 0; }	#!/bin/sh   if [ $# -lt 3 ]; then     echo "Usage: `basename $0` arg1 arg2 arg3" >&2     exit 1 fi   echo "arg1: $1" echo "arg2: $2" echo "arg3: $3" exit 0
	int main(int argc, char** argv) {     int i; for (i=1; i<=argc;i++) { printf(“arg:%s/n”,argv[i]); } return 0; }	#!/bin/sh   while [ $# -ne 0 ] do     echo "arg: $1"     shift done
逻辑/数值运算	if (d == 0)	if [ "$D" -eq "0" ] ; then
	if (d != 0)	if [ "$D" -ne "0" ] ; then
	if (d > 0)	if [ "$D" -gt "0" ] ; then
	if (d < 0)	if [ "$D" -lt "0" ] ; then
	if (d <= 0)	if [ "$D" -le "0" ] ; then
	if (d >= 0)	if [ "$D" -ge "0" ] ; then
字符串比较	if (strcmp(str,”abc”)==0) { }	if [ "$STR" != "abc" ]; then fi
输入和输出	scanf(“%d”,&D);	read D
	printf( “%d”, D);	echo –n $D
	printf( “%d”,D);	echo $D
	printf( “Press any to continue...”); char ch=getchar(); printf( “/nyou pressed: %c/n”, ch );	#!/bin/sh   getchar() { SAVEDTTY=`stty -g` stty cbreak dd if=/dev/tty bs=1 count=1 2> /dev/null stty -cbreak stty $SAVEDTTY }   echo -n "Press any key to continue..." CH=`getchar` echo "" echo "you pressed: $CH"
		read D <&3
程序/脚本的控制流程	if (isOK) {     //1 } else if (isOK2) {     //2 } else {     //3 }	if [ isOK ]; then     #1 elif [ isOK2 ]; then     #2 else     #3 fi
	switch (d) { case 1: printf(“you select 1/n”); break; case 2: case 3: printf(“you select 2 or 3/n”); break; default: printf(“error/n”); break; };	case $D in 1) echo "you select 1"     ;; 2|3) echo "you select 2 or 3"     ;; *) echo "error"     ;; esac
	for (int loop=1; loop<=5;loop++) {      printf( “%d”, loop); }	for loop in 1 2 3 4 5 do     echo $loop done
	do {     sleep(5); } while( !isRoot );	IS_ROOT=`who | grep root` until [ "$IS_ROOT" ] do     sleep 5 done
	counter=0; while( counter < 5 ) { printf( “%d/n”, counter); counter++; }	COUNTER=0 while [ $COUNTER -lt 5 ] do echo $COUNTER     COUNTER=`expr $COUNTER + 1` done
	while (1) { }	while : do done
	break;	break或break n，n表示跳出n级循环
	continue;	continue
函数与过程的定义	void hello() {     printf( “hello/n” ); } … //函数调用 hello();	hello() {     Echo “hello” } 或者 function hello() {     Echo “hello” } … #函数调用 hello
函数的参数和返回值	int ret = doIt(); if (ret == 0) {     printf( “OK/n” ); }	doIt if [ “$?” –eq 0 ] ; then echo “OK” fi 或者 RET = doIt if [ “$RET” –eq “0” ] ; then echo “OK” fi
	int sum(int a,int b) { return a+b; } int s = sum(1,2); printf(“the sum is: %d/n”, s);	sum() {     echo -n "`expr $1 + $2`" } S=`sum 1 2` echo "the sum is: $S"
	bool isOK() { return false; } if (isOK) {     printf( “YES/n” ); } else {     printf( “NO/n” ); }	isOK() {     return 1; } if isOK ; then     echo "YES" else     echo "NO" fi