Several ways to remove empty lines from a file with Unix utilities: Remove all empty lines with grep : cat test.txt | grep -v '^\s*$' or grep -v '^\s*$' test.txt Remove all empty lines with sed : sed '/^\s*$/d' test.txt Remove empty lines at the beginning of file with sed : sed '0,/\w/p' leadingBlankLines.txt | sed '0,/\w/d...

Got "base64: invalid input" error: $ base64 -d base64_encoded.txt >original.bin ba... which can be easily dismissed as "input is invalid base64 encoded" or "partial input". But I know it's valid base64 encoded input! The problem was, the input was base64 encoded on Windows! The error goes away after converting to Unix format with dos2unix . dos2unix < base64_encoded.txt | base64 -d >origina... Version of base64 used: $ base64 --version base64 (GNU coreutils) 8.5 ...

To remove new line characters from a file: with tr : tr -d '\n' < the-file.txt or cat the-file.txt | tr -d '\n' with sed : sed ':a;N;$!ba;s/\n//g' the-file.txt or cat the-file.txt | sed ':a;N;$!ba;s/\n//g' The sed version is a bunch of commands to manipulate the register etc. Regex replace " s/\n//g " does not work because sed regex works on a single line. More tips from this Linux blog: http://linux.dsplabs.com.au/rmnl-remove-new-line-characters-tr-awk-perl-sed-c-cpp-bash-python-xargs-ghc-ghci-haskell-sam-ssam-p65/

The Unix utility can convert a binary stream to hex and reverse it. The -p (or -ps ) switch means "plain", or "postscript" mode. $ cat >test.txt Line one Line two Line th...

grep is a versatile command with many variations (grep, egrep, fgrep, then various implementations). It uses a regula expression (regex) pattern to filter input. But then there are basic and extended flavors of regex - leading to even more confusion. And, beware that there are lots of bad examples of regex in the wild... There are two critical questions to ask when you use grep: which grep implementation are you using? what is the flavor of the regex? Here are some examples for gnu grep v2.7: # Find all numbers (no decimal point), basic regex... Use the -o flag to show only the matching part instead of the whole matching line: grep -o -E '\b[0-9]{2}\b' The good thing about the gnu grep is that it...

The Unix shell passes these parameters to the shell script: Variable Meaning $* A single string representing all command line arguments separated by $IFS (internal field separator, usually a space) $@ A sequence of strings representing the command line arguments. $1,$2...$n $1 is the first argument, $2 is the second argument, and so on... $0 The name of the script itself. $# The number of arguments. Example shell script ( sharg.sh ): #!/bin/sh echo $# arguments passed to $0: $@ ... Output for ./sharg.sh "a b c d" : 1 arguments passed to ./sharg.sh: a b c d here ... Output for ./sharg.sh a "b c" d : 3 arguments passed to ./sharg.sh: a b c d here ...

Use useradd to add a user (the switches are not required, but it's a good idea to give them. For example, without -m you'd create a user without a home directory): # -d switch specifies user home directory # -m ... You also need to use the passwd command to set a new password before the user can log in. To delete a user, use the userdel command: userdel demo

Variable Meaning $_ The default or implicit variable. @_ Within a subroutine the array @_ contains the parameters passed to that subroutine. $a, $b Special package variables when using sort() $<digit> Contains the subpattern from the corresponding set of capturing parentheses from the last pattern match, not counting patterns matched in nested blocks that have been exited already. $. Current line number for the last filehandle accessed. $/ The input record separator, newline by default. $| If set to nonzero, forces a flush right away and after every write or print on the currently selected output channel. Default is 0 (regardless of whether the channel is really buffered by the system or not; $| tells you only whether you've asked Perl explicitly to flush after...

The UNIX command xargs passes stdin to the command line. For example, to edit all files containing the word escape : grep -l escape * | xargs gvim

On Solaris or AIX, use truss . On Linux use strace . # trace the ls command strace ls # c... Some links: Unix process tracing patterns Debugging Unix processes: A Detective Story AIX 5.2 performance tools update, Part 2