Unix « MemoSoup

Reading password in Unix shell

print -n "Enter Your password:"
stty_orig=`stty -g`
trap "stty ${stty_orig}; exit" 1 2 3 15
stty -echo >&- 2>&-
read PASS
stty ${stty_orig} >&- 2>&-
trap 1 2 3 15
print

trap :catches interruptions. I.e. if the user presses Ctrl+C, the normal stty mode is set before stopping the program
stty -echo :switches off the display echo
>&- 2>&- :helps to avoid [...]

Unix shell: workaround for loop problem

It’s not possible to get the value of the loop variables in some versions of ksh.

Example:

#!/bin/ksh

num=0
cat $0 | while read line ; do
let num=num+1
done

echo "Number=$num"

This script will return “Number=0″ as the result on some Linux machines.

Here is the workaround for the problem: You should change the redirection method for the input file.

#!/bin/ksh

l=0
while read line ; do
let [...]

Unix: get the file date

ls -1 | cpio -o | cpio -ivt | awk ‘{print $NF, $(NF-1), $(NF-4), $(NF-3) }’

Warning: I/O expensive for the large files!

Perl:

@a = localtime((stat($my_file))[9]); [...]

Redirect script output to the log

If the whole output of the complex script should be redirected to the log, the following trick could be used.

if [ "$1" != "-log" ] ; then
$0 -log "$@" 2>&1 | tee the_log_file.$$.log [...]

grep in find command: how to display file names

Here is very simple trick to force the grep command to display file name, when it’s used together with find operation.
Just write /dev/null as the “second file”

find . -type f -exec grep somestring {} [...]

Using pattern lists in Unix

Here is the small reminder about the syntax of the “case” command and the usage of the pattern lists.

#!/bin/ksh
print -n "Please enter the line: "
read line

case "$line" in
?(dog|cat) ) print "zero or one occurrence of any pattern" ;;
*(low|high) ) print "zero or more occurrences of any pattern" ;;
@(duncan|methos) ) print "exactly one occurrence of any pattern" [...]

Print the PATH directories in the readable format

echo $PATH| awk -v RS=":" ‘{ print $0 }’

echo $LD_LIBRARY_PATH |awk -v RS=":" ‘{ system ( "ls -rltd " $0 ) }’

Warning!
As far as the option ‘-v’ is used, the new awk(nawk in some systems) should be used.

To check if the new version of awk is installed:

awk 1 /dev/null

The output will be empty for new awk.
You [...]

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