M<N M>N其中M為file descripter，N為某個檔案[?]。而如果要把fd導向給另一個fd，就要用下列格式：
M>&N其中M和N都是file descripter。
$ cat > test.c
#include <stdio.h>
int main( int argc, char * argv[] ) {
puts( "This is stdout." );
fputs( stderr, "This is stderr." );
return 0;
}
^D
$ gcc test.c -o test
$ ./test >output.txt 2>&1
$ ./test 2>&1 >output.txt
有趣的是，第一次在螢幕上什麼都沒顯示，而output.txt裡會找到那二個句子，但是第二次卻會在螢幕上顯示`This is stderr.'，output.txt只有`This is stdout.'。表面看起來結果至少要相反才對呀？
#! /usr/bin/env python
# -*- encoding: utf-8 -*-
import os, time, sys
def connect_test( *sites ):
for site in sites :
if os.system( "wget --tries=2 --timeout=120 -O - %s >/dev/null 2>&1" % site ) == 0 :
return True
return False
flog = open( '/var/log/firewall_fix.log', 'a' )
timestamp = time.strftime( '%Y/%m/%d %H:%M' )
if connect_test( 'http://www.google.com/' ):
print >> flog, "%s\tSuccess and do nothing.\n" % timestamp
else:
try:
if os.system( 'iptables-restore <%s >/dev/null 2>&1' % sys.args[1] ) != 0 :
raise OSError
else:
print >> flog, "%s\tFirewall fixed. ( Use `%s'. )\n" % ( timestamp, sys.args[1] )
except ( IndexError, OSError ):
os.system( 'iptables -F' )
for chain in [ 'INPUT', 'OUTPUT', 'FORWARD' ] :
os.system( "iptables -P %s ACCEPT" % chain )
print >> flog, "%s\tFirewall fixed. ( Flush all. )\n" % timestamp
flog.close()
#include <stdio.h>
#include <termios.h>
char getch(void) {
char buf = 0;
struct termios old = {0};
if (tcgetattr(0, &old) < 0)
perror("tcsetattr()");
old.c_lflag &= ~ICANON;
old.c_lflag &= ~ECHO;
old.c_cc[VMIN] = 1;
old.c_cc[VTIME] = 0;
if (tcsetattr(0, TCSANOW, &old) < 0)
perror("tcsetattr ICANON");
if (read(0, &buf, 1) < 0)
perror ("read()");
old.c_lflag |= ICANON;
old.c_lflag |= ECHO;
if (tcsetattr(0, TCSADRAIN, &old) < 0)
perror ("tcsetattr ~ICANON");
return (buf);
}
int main() {
char key;
printf("Press 'x' to exit...\n");
while((key=getch()) && (key != 'x'))
printf ("you pressed %c\n", key);
return(0);
}
Reference
gzip -cd file.gz | less
如果壓縮過之前還被封裝過，就要換個程式：
tar -ztf file.tar.gz | less
#! /bin/bash
if [ $# -eq 1 ] ; then # 只接受一個參數
if [[ $1 =~ '\.tar\.gz$' ]] ; then # 以regex過濾*.tar.gz
exec tar -ztf $1 | less
elif [[ $1 =~ '\.gz$' ]] ; then # 再過濾*.gz
exec gzip -cd $1 | less
else
echo 'Invalid filename.'
fi
else
echo 'Must takes one argument.'
fi
然後再把這個檔案改成可執行檔，export到PATH裡，就可以隨時取用了。