From 3e9196a08ed98f9d74cf4e8e0d3c02b3be3c8ef8 Mon Sep 17 00:00:00 2001
From: lara <lara@pixie>
Date: Tue, 22 Dec 2020 23:09:06 +0100
Subject: [PATCH] Add convenience function for shell scripting

---
 bin/rreadlink | 55 +++++++++++++++++++++++++++++++++++++++++++++++++++
 lib/utils.sh  | 24 ++++++++++++++++++++++
 2 files changed, 79 insertions(+)
 create mode 100755 bin/rreadlink
 create mode 100644 lib/utils.sh

diff --git a/bin/rreadlink b/bin/rreadlink
new file mode 100755
index 0000000..deb1aa1
--- /dev/null
+++ b/bin/rreadlink
@@ -0,0 +1,55 @@
+#!/bin/sh
+
+# Function by mklement0
+# https://stackoverflow.com/a/29835459/5309963
+# The following, POSIX-compliant shell function implements what
+# GNU's readlink -e does and is a reasonably robust solution
+# that only fails in two rare edge cases:
+# - paths with embedded newlines (very rare)
+# - filenames containing literal string -> (also rare)
+
+( # Execute the function in a *subshell* to localize variables and the effect of `cd`.
+
+  target=$1 fname= targetDir= CDPATH=
+
+  # Try to make the execution environment as predictable as possible:
+  # All commands below are invoked via `command`, so we must make sure that `command`
+  # itself is not redefined as an alias or shell function.
+  # (Note that command is too inconsistent across shells, so we don't use it.)
+  # `command` is a *builtin* in bash, dash, ksh, zsh, and some platforms do not even have
+  # an external utility version of it (e.g, Ubuntu).
+  # `command` bypasses aliases and shell functions and also finds builtins
+  # in bash, dash, and ksh. In zsh, option POSIX_BUILTINS must be turned on for that
+  # to happen.
+  { \unalias command; \unset -f command; } >/dev/null 2>&1
+  [ -n "$ZSH_VERSION" ] && options[POSIX_BUILTINS]=on # make zsh find *builtins* with `command` too.
+
+  while :; do # Resolve potential symlinks until the ultimate target is found.
+      [ -L "$target" ] || [ -e "$target" ] || { command printf '%s\n' "ERROR: '$target' does not exist." >&2; return 1; }
+      command cd "$(command dirname -- "$target")" # Change to target dir; necessary for correct resolution of target path.
+      fname=$(command basename -- "$target") # Extract filename.
+      [ "$fname" = '/' ] && fname='' # !! curiously, `basename /` returns '/'
+      if [ -L "$fname" ]; then
+        # Extract [next] target path, which may be defined
+        # *relative* to the symlink's own directory.
+        # Note: We parse `ls -l` output to find the symlink target
+        #       which is the only POSIX-compliant, albeit somewhat fragile, way.
+        target=$(command ls -l "$fname")
+        target=${target#* -> }
+        continue # Resolve [next] symlink target.
+      fi
+      break # Ultimate target reached.
+  done
+  targetDir=$(command pwd -P) # Get canonical dir. path
+  # Output the ultimate target's canonical path.
+  # Note that we manually resolve paths ending in /. and /.. to make sure we have a normalized path.
+  if [ "$fname" = '.' ]; then
+    command printf '%s\n' "${targetDir%/}"
+  elif  [ "$fname" = '..' ]; then
+    # Caveat: something like /var/.. will resolve to /private (assuming /var@ -> /private/var), i.e. the '..' is applied
+    # AFTER canonicalization.
+    command printf '%s\n' "$(command dirname -- "${targetDir}")"
+  else
+    command printf '%s\n' "${targetDir%/}/$fname"
+  fi
+)
diff --git a/lib/utils.sh b/lib/utils.sh
new file mode 100644
index 0000000..60ca9c2
--- /dev/null
+++ b/lib/utils.sh
@@ -0,0 +1,24 @@
+die() {
+    # Use notify-send to send errors when not in a terminal
+    # [ -t 0 ] only works outside of pipes
+    [ -t 0 ] || notify-send "$@" && >&2 echo "$@"
+    exit 1
+}
+
+# Output error to stderr and to graphical notification
+notify_err() {
+    tee /dev/fd/2 | xargs -n1 -d "\n" notify-send
+}
+
+assert_exists() {
+    for c in $@; do
+        which "$c" > /dev/null 2>&1 || die "$c doesn't appear to be installed"
+    done
+}
+
+check_exists() {
+    for c in $@; do
+        which "$c" > /dev/null 2>&1 || return 1
+    done
+}
+