Question

Bash Help Please. I need help with taking a txt document with commands and testing to see if they exist in bash. For example [clear], [zip]...ect are in the txt file. At the moment I have

for wordC in $(<commands.txt)
do

if [[ $command_wordC >/dev/null ]]; then

But it always goes to the else statement even if the command should exist. I thought about using Grep but im not entirely sure the purpose of it or how to use it correctly. Could anyone help please? Please explain if you use grep or any commands like that because im new to bash and would like to understand.

Answer 1

codeToCopy:

#!/bin/bash

#Reading each word from file

for wordC in $(<commands.txt)

do

# There is a built-in command to check whether a command exists or not.

# The 'type' command gives you the location of the script/executable

# of the specified command. If the command does not exist, it throws an error saying that

# command is not found. $wordC > /dev/null only redirects standard output. As we don't

# want to show the errors on the screen, appending(2>&1) the standard errors to standard output.

# 0 - represents standard input

# 1 - represents standard output

# 2 - represents standard error

# You are using '[[ ]]' to write if statement that actually uses 'test' command internal.

# Test command is mostly used to verify the expressions.

# You can use [[ ]], if you capture the output of the command inside if condition.

# ie. if [[ $(command) -eq "something" ]] and do the comparison.

# The below code is tested and does what you asked for.

if type $wordC >/dev/null 2>&1 ; then

echo "$wordC: Command exists!"

else

echo "$wordC: Command does not exist!"

fi

done

CodeScreenShot:

commandCheck.sh × commands.txt × #1 /bin/bash 3 #Reading each wo rd from file 4 for wordc in $(<commands.txt) 5 do # There is built-in command to check whether command exists or not. # The 'type command gives you the location of the script/executale # of specified command. If command does not exist, it throws an error saying that # command is not found. SordC > /dev/null only redirects standard output. As we don't # want to show the errors on the screen, appending (2X1) the standard errors to standard output. # -represents standard input # 1 - represents standard output # 2 - represents standard error # Actually in your code, you are using [[ ]] that internally uses test command # Test command is mostly used to verify the expressions. # You can use test command, if you capture the output of the command inside if condition. #ie. if [[ $(command) -eq "something" ]] and do the comparision. # The below code is tested. if type $wordc >/dev/null 2>&1; then 8 9 10 13 15 16 17 18 19 echo "$wordC: Command exists!" 21 else echo "$wordc: Command does not exist!" fi 25 done 26

commands.txt

clear zip
reset foo cat

Output Screenshot:

k@ashok-Aspire-E1-571G: /Desktop/Chegg ashok@ashok-Aspire-E1-571G: x ashok@ashok-Aspire-E ashok@ashok-Aspire-E1-571G:~/Desktop/Cheggs /commandCheck.sh clear: Command exists! zip: Conmand exists! reset: Command exists! foo: Command does not exist! cat: Command exists! ashok@ashok-Aspire-E1-571G:-/Desktop/Cheggs