CODEWITHSUNDEEP
bash
Chuck
Chuck

Reputation: 189

Bash script - If conditional with [ ]

I have the code below and am receiving the following error output: 

Enter your exam score
40
./if2.sh: line 6: 40: No such file or directory
Very well done. You have an A grade.

I'm using bash 4.1.2(1) on CentOS.

#!/bin/bash
#This script demonstrates the if-then-elif format.

echo "Enter your exam score"
read exam_pct
if [ $exam_pct < 40 ]
then
    echo "Sorry, you have failed."
elif [ $exam_pct > 70 ]
then 
    echo "Very well done. You have an A grade."
else
    echo "Well done. You passed."
fi

What's wrong here?

Upvotes: 2

Views: 949

Answers (4)

log0
log0

Reputation: 10917

Replace 

if [ $exam_pct < 40 ]

with

if (( exam_pct < 40 ))

Take a look at the link given by Bill. Unix shell history is full of non-intuitive extensions. Depending on your case, Bash should be safe to use though. If you are interested in shell history take a look at http://www.in-ulm.de/~mascheck/bourne/

Upvotes: 4

Diego Torres Milano
Diego Torres Milano

Reputation: 69198

Just for completeness:

if [ $exam_pct \< 40 ]

also works

Upvotes: 1

Cairnarvon
Cairnarvon

Reputation: 27752

To elaborate on why you're getting the error you're getting: [ isn't special syntax; it's just an executable (usually provided through a builtin, though /usr/bin/[ probably exists on your system), which by convention takes "]" as its last argument.

So when you write [ $exam_pct < 40 ], what you're actually doing is starting [ with (ideally) two arguments (the contents of $exam_pct, and ]), and the contents of a file with the name 40 piped to its stdin.

Similarly, when you do [ $exam_pct > 70 ], you're redirecting the output of [ $exam_pct ] (which will be blank, because [ doesn't ever write to stdout) to a file called 70.

Upvotes: 3

Bill
Bill

Reputation: 5764

if [ $exam_pct < 40 ] should be if [ "$exam_pct" -lt 40 ]

if [ $exam_pct > 70 ] should be if [ "$exam_pct" -gt 70 ]

Please always quote your variables.

Look at this for more details - http://tldp.org/LDP/abs/html/comparison-ops.html

Upvotes: 4

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