I have a changelog file in markdown which contains all changes between each version of my app like that :
## Version 1.0.6
* first change
* second change
* third change
## Version 1.0.5
* first foo change
* second foo change
## Version 1.0.4
* and so on...
What I want is to extract in a script the changes content for a version. For example I would to extract the changes for the version 1.0.5, so it should print :
* first foo change
* second foo change
The ideal way would be ./getVersionChanges version filename which would those 2 params :
version : the version to extract changes
filename : the filename to parse
How can I achieve this with sed, awk, grep, or whatever ?
A slightly more elaborate awk solution, which
awk -v ver=1.0.5 '
/^## Version / { if (p) { exit }; if ($3 == ver) { p=1; next } } p && NF
' file
As script getVersionChanges:
#!/usr/bin/env bash
awk -v ver="$1" '
/^## Version / { if (p) { exit }; if ($3 == ver) { p=1; next } } p && NF
' "$2"
Explanation:
Regex condition /^## Version / matches the header line of a block of lines with version-specific information, by looking for substring ## Version at the start (^) of the line and, if found, executing the associated code block ({ ... }):
if (p) { exit } exits (stops processing), if the p (print) flag has previously been set, because that implies that the block after the one of interest has been reached, i.e. that the block of interest has now been fully processed.
if ($3 == ver) { p=1; next } checks if the 3rd whitespace-separated field ($3) on the header line matches the given version number (passed via option -v ver=1.0.5 and therefore stored in variable ver) and, if so, sets custom variable p, which serves as a flag indicating whether to print a line, to 1 and moves on to the next line (next), so as not to print the header line itself.
In other words: p containing 1 indicates for subsequent lines that the version-specific block of interest has been entered, and that its lines should (potentially) be printed.
Condition p && NF implicitly prints the line at hand if the condition matches, which is the case if the print flag p is set and (&&) the line at hand has at least one field (based on the number of fields being reflected in built-in variable NF), i.e. if the line is non-blank, thereby effectively skipping empty and all-whitespace lines in the block of interest.
&& use implicit Boolean logic: a value of 0 (which a non-initialized custom variable such as p defaults to) is implicitly false, whereas any nonzero value implicitly true.