I’m starting with bash and I found the following:
if test $first -lt $second
then
echo $first is lower than $second
else
if test $first -gt $second
then
echo $first is higher than $second
else
echo $first and $second are equals
fi
fi
For reading the script and executing it, I know what it does, but not what -lt and -gt are for.
Can somebody tell me what is the name of that kind of ‘tool’ and what they(-lt and -gt) do? Thanks!
Answers:
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Method 1
It’s short for less than and greater than. It’s used for integer comparison in bash. You can read more by typing man test:
....
INTEGER1 -gt INTEGER2
INTEGER1 is greater than INTEGER2
....
INTEGER1 -lt INTEGER2
INTEGER1 is less than INTEGER2
....
Method 2
You can find the definition of -lt and -gt in the documentation of the test command (man test), or in the documentation of bash since test is a built-in command in bash (like in most other shells).
-lt and -gt are numeric comparisons (less-than [and not equal], greater-than [and not equal]). There are also less/greater-or-equal operators -le and -ge, and equal and not-equal operators -eq and -ne. These are numeric operators, so there will be an error if either side isn’t a number, and 9 is considered less than 10.
The reason names like -lt are used rather than the usual < is that the character < would be interpreted as a redirection. The operators = and != also exist, but they perform a string comparison: test 00 -eq 0 is true whereas test 00 = 0 is false.
Some shells, including bash, also have operators < and > which perform a string lexicographic comparison, so test 9 < 10 is false because 9 is sorted before 1 (the backslash prevents the character < from being interpreted as a redirection operator). These shells also offer the double-bracket syntax for tests, e.g. [[ 9 < 10 ]] (as opposed to [ 9 < 10 ]), which can’t have redirections inside so the < doesn’t need to be quoted.
Method 3
They are just operators.
Simply:
gt and lt mean > (greater than) and < (less than).
You can look here for more information on operators:
Method 4
These are comparison operators
-lt = less than
-gt = greater than
You can check this page for further details:
All methods was sourced from stackoverflow.com or stackexchange.com, is licensed under cc by-sa 2.5, cc by-sa 3.0 and cc by-sa 4.0