lib: add user_homedir and sponge functions

lib

@@ -80,3 +80,62 @@ epochseconds() {
     # TODO(andrew-d): break down and verify the math here
     echo $(( $(TZ=GMT0 date +"((%Y-1600)*365+(%Y-1600)/4-(%Y-1600)/100+(%Y-1600)/400+1%j-1000-135140)*86400+(1%H-100)*3600+(1%M-100)*60+(1%S-100)") ))
 }
+
+# user_homedir returns the home directory for the provided user
+user_homedir() {
+    local user="$1"
+
+    awk \
+        -v u="$user" \
+        -v FS=':' \
+        '$1==u {print $6}' \
+        /etc/passwd
+}
+
+# sponge acts like sponge(1) from moreutils, but is portable.
+#
+# It "soaks up" all input from stdin before writing it to the specified output;
+# helpful for modifying a file in-place with a utility that does not support
+# it.
+sponge() {
+    local append=false
+
+    while getopts 'a' opt; do
+        case $opt in
+            a) append=true ;;
+            *) echo "unknown option: $opt" >&2; exit 1;;
+        esac
+    done
+    shift "$(( OPTIND - 1 ))"
+
+    local outfile="$1"
+    local tmpfile
+
+    tmpfile="$(mktemp "$(dirname "$outfile")/tmp-sponge.XXXXXXXX")" &&
+    cat >"$tmpfile" &&
+    if "$append"; then
+        cat "$tmpfile" >>"$outfile"
+    else
+        if [ -f "$outfile" ]; then
+            # NOTE: the stat() call here isn't exactly portable, but both GNU
+            # coreutils and busybox support it, so close enough? Let's
+            # double-check that it returns something sensible just to be sure.
+            local oldperms
+            oldperms="$(stat -c '%a' "$outfile")"
+
+            if [ "${#oldperms}" = "3" ] && [ -z "$(echo "$oldperms" | tr -d '0-9')" ]; then
+                chmod "$oldperms" "$tmpfile"
+            else
+                printf "warning (bad: %s): not setting permssions on: %s\n" "${oldperms}" "$outfile" >&2
+            fi
+        fi
+        if [ -f "$outfile" ]; then
+            mv "$tmpfile" "$outfile"
+        elif [ -n "$outfile" ] && [ ! -e "$outfile" ]; then
+            cat "$tmpfile" >"$outfile"
+        else
+            cat "$tmpfile"
+        fi
+    fi &&
+    rm -f "$tmpfile"
+}

test/lib_test.sh

@@ -95,5 +95,48 @@ testEpochseconds() {
     assertEquals "" "$(epochseconds | tr -d '[0-9]')"
 }
 
+testUserHomedir() {
+    assertEquals "$HOME" "$(user_homedir "$USER")"
+}
+
+testSponge() {
+    for i in $(seq 1 10000); do
+        echo "i am a test line of length 30" >> "$TEST_TMPDIR/largefile.txt"
+        echo "i am a neat line of length 30" >> "$TEST_TMPDIR/expected.txt"
+    done
+
+    # Modify the file; if we don't sponge, this will probably overwrite things
+    # and won't work.
+    cat "$TEST_TMPDIR/largefile.txt" | \
+        sed 's/test/neat/g' | \
+        sponge "$TEST_TMPDIR/largefile.txt"
+
+    # The files should be equal (currently, we just compare CRCs)
+    assertEquals "$(cksum < "$TEST_TMPDIR/largefile.txt")" "$(cksum < "$TEST_TMPDIR/expected.txt")"
+}
+
+testSponge_Permissions() {
+    echo "i am the input file" > "$TEST_TMPDIR/input.txt"
+    echo "i am the output file" > "$TEST_TMPDIR/output.txt"
+
+    # Set a strange permission on the output file that we will replicate.
+    chmod 0741 "$TEST_TMPDIR/output.txt"
+
+    cat "$TEST_TMPDIR/input.txt" | sponge "$TEST_TMPDIR/output.txt"
+
+    # The files should be equal
+    assertEquals "$(cat "$TEST_TMPDIR/input.txt")" "$(cat "$TEST_TMPDIR/output.txt")"
+    assertEquals "741" "$(stat -c '%a' "$TEST_TMPDIR/output.txt")"
+}
+
+testSponge_Append() {
+    echo "one" > "$TEST_TMPDIR/input.txt"
+    echo "two" > "$TEST_TMPDIR/output.txt"
+
+    cat "$TEST_TMPDIR/input.txt" | sponge -a "$TEST_TMPDIR/output.txt"
+
+    assertEquals "$(printf 'two\none\n')" "$(cat "$TEST_TMPDIR/output.txt")"
+}
+
 # Load shUnit2
 . ./shunit2