Comparisons in Shell

Question

I am trying to write a program that checks whether the number stored in a file (variable n) + 8 is greater or equal to 100. If it is, terminate, else, add 8 and store back in file. However, when I try running it, it says the command in line 4 (if condition) cannot be found. Can someone please explain to me why this isn't working? Thanks.

#!/bin/bash
n=$(cat test.txt)
if [$(($n+8)) -ge 100]
then
    echo 'terminated program' > test.txt
else
    m=$(($n+3))
    echo $m > test.txt
fi

BTW, http://shellcheck.net/ would have identified this issue automatically. — Charles Duffy, Mar 08 '18 at 22:13
If the file is only supposed to contain a single number on one line, just use `read n < test.txt`. — chepner, Mar 09 '18 at 12:48

Gilles Quénot · Answer 1 · 2018-03-08T23:03:47.330

3

You miss some spaces :

if [$(($n+8)) -ge 100]

->

if [ $(($n+8)) -ge 100 ]

But while using bash, prefer a modern solution, using bash arithmetic :

if (( n+8 >= 100 ))

or even

if ((n+8>=100))

Like @Gordon Davisson said in comments : arithmetic contexts like inside (( )) are one of the few places in bash where spaces aren't critical delimiters.

edited Mar 08 '18 at 23:03

answered Mar 08 '18 at 22:00

Gilles Quénot

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Thanks! forgot spacing matters in bash. – M.Ahmed Mar 08 '18 at 22:02
Right. `[` is actually a **command**. See `help [` at a bash prompt. And like any command, it needs spaces to separate it from its arguments. Keep in mind that the next word after `if` is a command. – glenn jackman Mar 08 '18 at 22:10
1

Note: arithmetic contexts like inside `(( ))` are one of the few places in bash where spaces aren't critical delimiters. – Gordon Davisson Mar 08 '18 at 22:55

Comparisons in Shell

1 Answers1