Other useful command：
1. nm –list symbols from object files
2. ar crv libfoo.a bill.o foo.o
gcc –o hello hello.c libfoo.a
or gcc –o hello hello.c –L. –lfoo
Redirect：
Redirecting output:
$ls –al > output.txt (if output.txt exist: overwriting the output.txt
$ls –al >> output.txt(if output.txt exist, append the output.text)
$ kill -HUP 1234 >killout.txt 2>killerr.txt (will put the output and error information into separate files.)
$ kill -1 1234 >killouterr.txt 2>&1(f you prefer to capture both sets of output into a single file, you can use the >& operator to combine the two outputs. Therefore,)
$ kill -1 1234 >/dev/null 2>&1 (you don’t often want to save either standard output or standard error. You can use the Linux universal “bit bucket” of /dev/null to efficiently discard the entire output, like this:)
Redirecting input:
Rather like redirecting output, you can also redirect input. For example,
$ more < killout.txt