Correctly handle an arbitrary number of lines in PS0 rewriting

README.md

This is a small revision to the move_cursor_to_start_of_ps1 function described in ‘When did I run that command?’. The original relies on a specific number of lines in PS1; this works with an arbitrary number of lines.

The original code works correctly for the PS1 provided in the article, but my PS1 has an additional line, and I wanted to avoid using a magic number in case I change my PS1 in the future.

move_cursor_to_start_of_ps1.diff

diff --git a/Users/jordancole/1.txt b/Users/jordancole/2.txt
index 29a1fcd..0421ec7 100644
--- a/Users/jordancole/1.txt
+++ b/Users/jordancole/2.txt
@@ -1,14 +1,24 @@
 move_cursor_to_start_of_ps1() {
+    local lines
     command_rows=$(history 1 | wc -l)
     if [ "$command_rows" -gt 1 ]; then
-        let vertical_movement=$command_rows+1
+        lines=$command_rows
     else
         command=$(history 1 | sed 's/^\s*[0-9]*\s*//')
         command_length=${#command}
         ps1_prompt_length=${#PS1_PROMPT}
         let total_length=$command_length+$ps1_prompt_length
         let lines=$total_length/${COLUMNS}+1
-        let vertical_movement=$lines+1
     fi
+    # The timestamp placeholder may not be on the first line of PS1, and PS1
+    # may be more than 1-2 lines. This uses sed to strip out everything before
+    # the placeholder, then gets the number of lines with wc. Note that if
+    # $TIMESTAMP_PLACEHOLDER contains '/' this sed command will fail -- in that
+    # case the '/'s in the command will need to be replaced with a different
+    #  delimiter. (I often use ':', e.g. "sed 's:xx:yy:'", but
+    # $TIMESTAMP_PLACEHOLDER contains ':'.)
+    ps1_lines="$(echo "$PS1" | sed -E "s/.+$TIMESTAMP_PLACEHOLDER//" | grep --fixed-strings "\n" --only-matching | wc -l)"
+    let vertical_movement=lines+ps1_lines
+
     tput cuu $vertical_movement
 }