Different syntax for if in shell script

Question

I am learning shell script and I find different syntax for shell script conditional statements. Does csh script have a different syntax than tcsh script. Some say

 if [ "$PASSWORD" == "$VALID_PASSWORD" ]; then
echo "You have access!"
 else
echo "ACCESS DENIED!"
  fi

some use

 if ($PASSWORD == $VALID_PASSWORD)
 echo "You have access!"
 else
echo "ACCESS DENIED!"
 endif

I tried my own and I get errors like "if: Empty if" or "If: Expression Syntax" and these messages are very brief to understand. So I thought of asking how to sort out these issues and are there solutions different based on shell (csh, tcsh)

If my shell is tcsh, should I always tcsh script or can I write bash script.

As Carl's answer says, you can write scripts using whatever shell you like, regardless of what shell you use interactively. But read this: perl.com/doc/FMTEYEWTK/versus/csh.whynot — Keith Thompson
– Keith Thompson, Commented Jun 21, 2013 at 22:00
Thanks Thompson .. I am just learning to program shells and I can learn bash shell than csh shell scripting — Raghav
– Raghav, Commented Jun 21, 2013 at 22:21

Carl Norum · Accepted Answer · 2013-06-21 17:54:13Z

4

csh and tcsh share the same syntax for an if statement:

if (expr) then
...
else if (expr2) then
...
else
...
endif

Your other example is (probably) from sh or bash:

if list; then list; [ elif list; then list; ] ... [ else list; ] fi

Where your list happens to be an invocation of the program (or sometimes shell builtin) [.

You can write scripts for whatever shell you want as long as you put the right one of

#!/bin/sh
#!/bin/bash
#!/bin/csh
#!/bin/tcsh

to match your script's intended shell at the top of the file.

answered Jun 21, 2013 at 17:54

Carl Norum

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4 Comments

Raghav Over a year ago

The error I got for following code is "if : Empty if" if ( $1 == "one") echo "one" else if ($1 == "two") echo "two" else echo " no proper input" endif when executed as ./script one

Gordon Davisson Over a year ago

@Raghav that's because your if statement is missing its then keyword.

Raghav Over a year ago

Thanks Gordon .. I did not know if and then should be in same line.. Now code is working

Keith Thompson Over a year ago

csh and tcsh also permit a limited single-line if statement: if (expr) stmt (distinguished by the lack of a then) -- but that form doesn't permit an else.

Michael Gaskill · Accepted Answer · 2017-02-06 10:16:19Z

0

This is the actual script for that -

#!/bin/sh
# This is some secure program that uses security.

VALID_PASSWORD="secret" #this is our password.

echo "Please enter the password:"
read PASSWORD

if [ "$PASSWORD" == "$VALID_PASSWORD" ]; then
    echo "You have access!"
else
    echo "ACCESS DENIED!"
fi

edited Feb 6, 2017 at 10:16

Michael Gaskill

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answered Apr 16, 2014 at 14:35

Akshay

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