posix: always seek to EOF when opening a file in append mode Python 3 already does this, so skip it there. Consider the program: #include <stdio.h> int main() { FILE *f = fopen("narf", "w"); fprintf(f, "narf\n"); fclose(f); f = fopen("narf", "a"); printf("%ld\n", ftell(f)); fprintf(f, "troz\n"); printf("%ld\n", ftell(f)); return 0; } on macOS, FreeBSD, and Linux with glibc, this program prints 5 10 but on musl libc (Alpine Linux and probably others) this prints 0 10 By my reading of https://pubs.opengroup.org/onlinepubs/009695399/functions/fopen.html this is technically correct, specifically: > Opening a file with append mode (a as the first character in the > mode argument) shall cause all subsequent writes to the file to be > forced to the then current end-of-file, regardless of intervening > calls to fseek(). in other words, the file position doesn't really matter in append-mode files, and we can't depend on it being at all meaningful unless we perform a seek() before tell() after open(..., 'a'). Experimentally after a .write() we can do a .tell() and it'll always be reasonable, but I'm unclear from reading the specification if that's a smart thing to rely on. This matches what we do on Windows and what Python 3 does for free, so let's just be consistent. Thanks to Yuya for the idea.

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#!/usr/bin/env bash

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# A simple script for opening merge conflicts in the editor.

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# Use the following Mercurial settings to enable it.

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#

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# [ui]

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# merge = editmerge

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#

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# [merge-tools]

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# editmerge.args=$output

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# editmerge.check=changed

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# editmerge.premerge=keep

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FILE="$1"

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getlines() {

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  grep -n "^<<<<<<" "$FILE" | cut -f1 -d:

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}

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# editor preference loosely based on https://mercurial-scm.org/wiki/editor

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# hg showconfig is at the bottom though, since it's slow to run (0.15 seconds)

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ED="$HGEDITOR"

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if [ "$ED" = "" ] ; then

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  ED="$VISUAL"

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fi

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if [ "$ED" = "" ] ; then

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  ED="$EDITOR"

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fi

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if [ "$ED" = "" ] ; then

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  ED="$(hg showconfig ui.editor)"

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fi

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if [ "$ED" = "" ] ; then

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  echo "merge failed - unable to find editor"

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  exit 1

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fi

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if [ "$ED" = "emacs" ] || [ "$ED" = "nano" ] || [ "$ED" = "vim" ] ; then

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  FIRSTLINE="$(getlines | head -n 1)"

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  PREVIOUSLINE=""

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  # open the editor to the first conflict until there are no more

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  # or the user stops editing the file

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  while [ ! "$FIRSTLINE" = "" ] && [ ! "$FIRSTLINE" = "$PREVIOUSLINE" ] ; do

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    $ED "+$FIRSTLINE" "$FILE"

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    PREVIOUSLINE="$FIRSTLINE"

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    FIRSTLINE="$(getlines | head -n 1)"

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  done

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else

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  $ED "$FILE"

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fi

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# get the line numbers of the remaining conflicts

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CONFLICTS="$(getlines | sed ':a;N;$!ba;s/\n/, /g')"

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if [ ! "$CONFLICTS" = "" ] ; then

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  echo "merge failed - resolve the conflicts (line $CONFLICTS) then use 'hg resolve --mark'"

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  exit 1

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fi

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exit 0