Bash

Process And Stream | Useful Commands | Essential Commands | Scripts | .bashrc

Here some useful commands. We suppose you are using the bash shell, if not, simply type: bash.

Process And Stream :

On bash, the .bashrc file is used to configure your environnment.

Process Management :

• A &: Make a new process running the A command.
• A && B: Mean we try the A command and if it is a success we try the B command.
• A || B: Mean we try the B command only if A is a failure.
• A `B`: Run the B command and add the result as a A parameter.
• A $(B): Run the B command and add the result as a A parameter.

Stream management :

It exists 3 main streams :

• The standard input (Entry 0)
• The standard output (Entry 1)
• The error output (Entry 2)

Here a standard way to use these streams :

• A > result1: Run the A command and write the output in the result1 file
• A 2> result1 : Run the A command and write the error output in the result1 file
• A > result1 2>&1 : Mean run the A command and write the standard output and the error output in a file result1.
• A < commands: Run the A command and propose the commands file as A caracters input.
• A | B: Run the A command and send its output to the input of B

A little Tip on the A command :

• if you don't wish to see the standard output, write : A >/dev/null,
• If you don't wish to see the sandard output and the error output : A 2>&1 >/dev/null,
• If you don't wish to see the error output : A 2>/dev/null

Useful Commands

      for file in *; do
       if ( grep 'AA' $file ); then
         echo $file contains the AA string 
       fi
      done
      

 
      for PID in $(ps); do
        if ( echo $PID | grep 'java' ); then
	  toKill=$( echo $PID | cut -f 2 -d ' ' );
	  echo Kill the process $toKill
	  kill -9 $toKill
	fi
      done
      

Essential Commands

a. Find a MOTIF in all file from the current directory

find . -type f | xargs grep MOTIF

b. Search and replace a MOTIF in all file from the current directory

# Be careful with such command
# It creates a temporary file with the good motif and
# replace the old file by this one.
# It is really dangerous to use the same stream for reading and writing
# That's why the temporary file is used

for file in $(find . -type f); do
  sed 's/OLDMOTIF/NEWMOTIF/g' < $file > $file.tmp
  rm -f $file
  mv $file.tmp $file
done

c. Count the number of file containing a MOTIF from the current directory

# Walk through the current directory and 
# update the count variable each time the
# MOTIF is found

declare -i count=0;
for file in $(find . -type f); do
 if ( grep MOTIF <$file >/dev/null 2>&1 ); then
  count=$((count+1)); 
 fi
done

echo $count files for MOTIF

.bashrc :

The .bashrc is a file that contains your configuration preference (for the bash shell only !). It is located at your personnal home directory.

Here's a sample :