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Updated SC2308 (markdown)

Eisuke Kawashima
2025-07-29 10:38:15 +09:00
parent 5c9f6c8244
commit 4daacaa809
1 changed files with 5 additions and 4 deletions
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9
SC2308.md

@@ -39,6 +39,7 @@ col2="${str:7:5}"
# Get substring by index (POSIX) # Get substring by index (POSIX)
col2="$(printf 'foo bar baz\n' | cut -c 8-12)" col2="$(printf 'foo bar baz\n' | cut -c 8-12)"
``` ```
### Rationale: ### Rationale:
You are using a `expr` with `length`, `match`, `index`, or `substr`. These forms did not make it into POSIX, and fail on platforms like MacOS and FreeBSD. Consider replacing them with portable equivalents: You are using a `expr` with `length`, `match`, `index`, or `substr`. These forms did not make it into POSIX, and fail on platforms like MacOS and FreeBSD. Consider replacing them with portable equivalents:
@@ -52,7 +53,7 @@ can be trivially replaced with the POSIX form `expr str : regex`
#### `index` #### `index`
if you only need a numerical index as part of trying to extract a piece of the string, consider replacing it with parameter expansion: if you only need a numerical index as part of trying to extract a piece of the string, consider replacing it with parameter expansion:
``` ```sh
str="mykey=myvalue" str="mykey=myvalue"
key="${str%%=*}" # Remove everything after first =, no index required key="${str%%=*}" # Remove everything after first =, no index required
value="${str#*=}" # Remove everything before first =, no index required value="${str#*=}" # Remove everything before first =, no index required
@@ -60,7 +61,7 @@ value="${str#*=}" # Remove everything before first =, no index required
otherwise, you can find the index of the first `=` using parameter expansion and string length: otherwise, you can find the index of the first `=` using parameter expansion and string length:
``` ```sh
str="mykey=myvalue" str="mykey=myvalue"
x=${str%%=*} # Assign x="mystr" x=${str%%=*} # Assign x="mystr"
index=$((${#x}+1)) # Add 1 to length of x index=$((${#x}+1)) # Add 1 to length of x
@@ -70,14 +71,14 @@ index=$((${#x}+1)) # Add 1 to length of x
Extract a substring via character index is generally fragile. For example, in this example, any minor changes to the format, including just the version increasing from 8.9 to 8.10, will cause the following snippet to fail: Extract a substring via character index is generally fragile. For example, in this example, any minor changes to the format, including just the version increasing from 8.9 to 8.10, will cause the following snippet to fail:
``` ```sh
str="VIM - Vi IMproved 8.2 (2019 Dec 12, compiled Feb 15 2021 12:29:39)" str="VIM - Vi IMproved 8.2 (2019 Dec 12, compiled Feb 15 2021 12:29:39)"
version=$(expr substr "$str" 19 3) version=$(expr substr "$str" 19 3)
``` ```
Instead, consider a different approach: Instead, consider a different approach:
``` ```sh
x="${str%% (*}" # Delete ` (` and everything after, giving "VIM - Vi IMproved 8.2" x="${str%% (*}" # Delete ` (` and everything after, giving "VIM - Vi IMproved 8.2"
version="${x##* }" # Delete everything before last space, giving "8.2" version="${x##* }" # Delete everything before last space, giving "8.2"