2.1   2007-05-11 how to distinguish $1 in shell and awk

$1 in shell is position variable, while in awk it's field variable.

use prime. If awk's command is wrapped by prime, wrapping $1 with prime turns it into shell position variable:

func() {
awk 'NR=='$2' {print $'$1'}' $3
}

(use it as)
func 6 400 /etc/password

use double-quote and anti-slash. In double-quoted commandline, $1 means shell position variable while $1 means awk field variable:

awk "{if (\$4>$cutoff) print \$2,$i,\$3}" data.file

(2006-08-20) When awk is used in command substitution, only the first approach works. The shell variable could also be used similar as the position variable. But it only works when the shell variable's value is number, otherwise, it displays nothing.:

var=`awk 'NR=='$shell_var' {print $1}' data.file`

2.2   2009-6-19 select certain lines of a file

For example, select all lines which is not at line 149 and 108:

awk 'NR!=149 && NR!=108 {print}' /tmp/call_method_42_uniq_1st_3_column.tsv

2.3   2009-7-30 change the suffix of files

For example, change all *.cc to *.c:

for i in `ls *.cc`; do name=`echo $i| awk 'BEGIN {FS="."} {print $1}'`; echo $name;  mv $name.cc $name.c ; done

5.1   bc

bc is an arbitrary precision calculator language

without any argument, it opens a interactive environment. Otherwise, the argument is treated as an input filename. Use pipe to let bc read from stdin

echo 3 + 1|bc

5.2   python

similar strategy. use pipe to redirect input to stdin.:

echo 'print 3+1'|python