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In Bash I can write the following test
[[ "f" > "a" ]] which results in returning 0, i.e. true. How does bash actually perform this string comparison? From my understanding > does an integer comparison. Does it try to compare the ASCII value of the operands?
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When comparing strings in Bash you can use the following operators: string1 = string2 and string1 == string2 - The equality operator returns true if the operands are equal. Use the = operator with the test [ command. Use the == operator with the [[ command for pattern matching.
Using String. equals() :In Java, string equals() method compares the two given strings based on the data/content of the string. If all the contents of both the strings are same then it returns true. If any character does not match, then it returns false.
In a Bash script, you'd normally be storing one or both of your strings as variables before comparing them. In this example, we are using the = operator and an if statement to determine if the two strings are equal to each other.
Details. Use == operator with bash if statement to check if two strings are equal. You can also use != to check if two string are not equal.
From help test:
STRING1 > STRING2 True if STRING1 sorts after STRING2 lexicographically. Internally, bash either uses strcoll() or strcmp() for that:
else if ((op[0] == '>' || op[0] == '<') && op[1] == '\0') { if (shell_compatibility_level > 40 && flags & TEST_LOCALE) return ((op[0] == '>') ? (strcoll (arg1, arg2) > 0) : (strcoll (arg1, arg2) < 0)); else return ((op[0] == '>') ? (strcmp (arg1, arg2) > 0) : (strcmp (arg1, arg2) < 0)); } The latter actually compares ASCII codes, the former (used when locale is enabled) performs a more specific comparison which is suitable for sorting in given locale.
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It's an alphabetical comparison (AIUI the sort order may be influenced by the current locale). It compares the first character of each string, and if the one on the left has a higher value it's true, if lower it's false; if they're the same, then it compares the second character, etc.
This is not the same as integer comparison, for that you use [[ 2 -gt 1 ]] or (( 2 > 1 )). To illustrate the difference between string and integer comparison, consider that all of the following are "true":
[[ 2 > 10 ]] # because "2" comes after "1" in ASCII sort order [[ 10 -gt 2 ]] # because 10 is a larger number than 2 (( 10 > 2 )) # ditto Here are some more test that're true as string comparisons, but would be false with integer comparison:
[[ 05 < 5 ]] # Because "0" comes before "5" [[ +5 < 0 ]] # Because "+" comes before the digits [[ -0 < 0 ]] # Because "-" comes before the digits [[ -1 < -2 ]] # Because "-" doesn't change how the second character is compared If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
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