These are some random Unix/Linux commands that we have come across and thought will be useful for tech enthusiasts,
#1 While writing a shell script if you would like to log the output of each and every command execution it is a good idea to have the script started with exec statement so that the total script output can be logged,
exec > /path/logfile.log 2>&1
Here , File descriptor 1 is the standard output
File descriptor 2 is the standard error
#2 typeset variable type
typeset is variable type that is used to hold a value pulled from a text file or a command output. Basically we are not pulling/assigning a value directly but it is being the result of a command or set of commands
For ex : Let's assume there is a txt file as below with three rows
check.txt
----------------------------------
LX1 T LICENSE Test1
LX2 M LICENSE Test2
LX3 P LICENSE Test4
I would like to pull the 2nd and 4th column values from row 2 that has Test2 and then assign those values to col1 variable then here it is ,
typeset col1=`grep 'Test2' /check.txt | awk '{ print $2 , $4}'`
If the row has to be separated by field separator before printing the values then we use 'FS'
typeset col2=`grep 'Test2' /check.txt | awk 'BEGIN {FS = " "} { print $2 }'`
If at all we want a substring of a value
typeset col3=`grep 'Test2' /check.txt | awk '{ print substr($3, 3, 5) }'`
As per need the typeset variables can be echo'ed.
echo ++ col1 is ${col1}
Below is another way to use typeset variable,
typeset col4= `echo check.txt | awk 'BEGIN {FS = "/" } { print $4 }'`
#3 AWK commands
we have seen a couple awk commands in the above examples, here are some other,
date | awk ' BEGIN { print "Today date is " } OFS="/" {print $2,$3,$NF }'
who | awk '$1 == "owner" {print "Owner Name is " $1 , $2 }'
#4 While loop
Using while loop to read lines of a file and apply various operations on them
Let's say there is a file with name check.txt
IN_FILE=check.txt
while read LINE
do
typeset CHECK_VAR=`echo ${LINE} | awk '{FS=","} {print substr($1,1,4)}' ` #2016
typeset CHECK_VAR_YEAR=`echo ${LINE} | awk '{FS=","} {print substr($1,3,2)}' `
done < ${IN_FILE}
