Multiple conditions in ShellScripting

Question

This is my Shellscript

echo "IsInteractive"
read IsInteractive
if [ "$IsInteractive" == "true" ]; then
 echo "Name"
 read name
 echo "Password"
 read password
 if [ "$name" == "abcd" & "$password" == "pwd" ]; then
  echo "correct username and password"
 else
  echo "wrong username or password"
 fi
elif [ "$IsInteractive" == "false" ]; then
 echo "Everything working fine.But no logic given yet"
else
 echo "Give proper input"
fi

Is there something wrong in the 2nd if-condition?I tried putting && in the condition,but didn't work

ghostdog74 · Accepted Answer · 2011-04-26 04:52:41Z

4

You don't use multiple condition inside square brackets as &, you use -a. Or you use multiple brackets if [ $a = "a" ] && [ $b = "c" ] You can also use the case/esac construct , eg

case "$name$password" in
 "abcdpwd" ) echo "correct" ;;
  *) echo "not correct";;
esac

This is much cleaner than if/else IMO.

answered Apr 26, 2011 at 4:52

ghostdog74

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corlettk Over a year ago

The case construct also supports wildcards in its "case labels"... so "abc*pwd" ) matches any string that begins with "abc" and ends with "pwd"... which can be REALLY handy for matching filenames (with extensions)... And that's exactly what the *) in the above example means... * by itself matches ANY string, including the empty (zero length) string!

jcomeau_ictx · Accepted Answer · 2011-04-26 04:51:10Z

3

Inside square brackets -a is the equivalent to &&

Also, you should probably be using = not ==. Read the manpage for your shell.

answered Apr 26, 2011 at 4:51

jcomeau_ictx

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1 Comment

jcomeau_ictx Over a year ago

@William Pursell: according to the Bash manpage, only for POSIX conformance.

corlettk · Accepted Answer · 2011-04-26 08:42:48Z

if [ "$name" == "abcd" -a "$password" == "pwd" ]; then echo true; else echo false; fi

This and MANY more "basic" questions can be answered quickly and without the need for a forum-post with the command man bash on most systems; and if it's not there just google "man bash" and pick the one which seems closest to your system... they're all "pretty much the same", especially at the basic level.

Cheers. Keith.

EDIT: FWW: the [ ] construct is a short-cut for "test", a function which is built-into all the the "standard" shells (sh, csh, ksh, and bash)... so the following code is EXACTLY equivalent:

$ a=a
$ b=c
$ if test "$a" = "a" && test "$b" = "c"; then echo true; else echo false; fi
true

The if then construct just evaluates the return value from the test function. You can display the return value of your last shell command with $?... but beware, echo also sets $?:

$ true
$ echo $?
0

$ false
$ echo $?
1
$ echo $?
0

The really interesting ramification of that is that the if then construct can evaluate anything which returns success=0=true or failure=anything BUT 0 (typically 1=false)... be that a shell built-in function, a user-defined function, a unix utility or a program you wrote yourself. Hence the following code is roughly equivalent:

$ if echo "$a:$b" | fgrep -s "a:c"; then echo true; else echo false; fi
a:c
true

NOTE: looks like my system's fgrep doesn't accept the -s for silent switch. Sigh.

Note that in above example, where the output from echo is being piped to the standard fgrep utility, it is the return value of fgrep (the LAST command to be invoked) which is evaluated by if then.

Good luck, and may root be with you. Cheers again. Keith.

implmentor · Accepted Answer · 2015-08-18 07:50:55Z

0

A minor change will resolve this scripting error [: missing `]'. At line 8 replace '&' with '-a' -a, the logical AND. If both the operands are true then condition would be true otherwise it would be false

Working code below

echo "IsInteractive"
read IsInteractive
if [ "$IsInteractive" == "true" ]; then
    echo "Name"
    read name
    echo "Password"
    read password
    if [ "$name" == "abcd" -a "$password" == "pwd" ]; then
        echo "correct username and password"
    else
        echo "wrong username or password"
    fi
elif [ "$IsInteractive" == "false" ]; then
    echo "Everything working fine.But no logic given yet" 
else
    echo "Give proper input"
fi

edited Aug 18, 2015 at 7:50

implmentor

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answered Aug 18, 2015 at 7:30

Baiju Chandran

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