Add swr(1df)

3 files changed, 104 insertions, 0 deletions

diff --git a/README.markdown b/README.markdown
index 984c6378..39bc3666 100644
--- a/README.markdown
+++ b/README.markdown
@@ -489,6 +489,8 @@ Installed by the `install-bin` target:
 *   `sue(8df)` execs `sudoedit(8)` as the owner of all the file arguments given,
     perhaps in cases where you may not necessarily have `root` `sudo(8)`
     privileges.
+*   `swr(1df)` allows you to run commands locally specifying remote files in
+    `scp(1)`'s HOST:PATH format.
 *   `td(1df)` manages a to-do file for you with `$EDITOR` and `git(1)`; I used
     to use Taskwarrior, but found it too complex and buggy.
 *   `try(1df)` repeats a command up to a given number of times until it
diff --git a/bin/swr b/bin/swr
new file mode 100755
index 00000000..56ab5919
--- /dev/null
+++ b/bin/swr
@@ -0,0 +1,65 @@
+#!/bin/sh
+# Transparently wrap scp(1) targets on the command line
+self=swr
+
+# Create a temporary directory with name in $td, and handle POSIX-ish traps to
+# remove it when the script exits.
+td=
+cleanup() {
+    [ -n "$td" ] && rm -fr -- "$td"
+    if [ "$1" != EXIT ] ; then
+        trap - "$1"
+        kill "-$1" "$$"
+    fi
+}
+for sig in EXIT HUP INT TERM ; do
+    # shellcheck disable=SC2064
+    trap "cleanup $sig" "$sig"
+done
+td=$(mktd "$self") || exit
+
+# Set a flag to manage resetting the positional parameters at the start of the
+# loop
+n=1
+for arg ; do
+
+    # If this is our first iteration, reset the shell parameters
+    case $n in
+        1) set -- ;;
+    esac
+
+    # Test whether this argument looks like a remote file
+    if (
+
+        # Test it contains a colon
+        case $arg in
+            *:*) ;;
+            *) exit 1 ;;
+        esac
+
+        # Test the part before the first colon has at least one character and
+        # only hostname characters
+        case ${arg%%:*} in
+            '') exit 1 ;;
+            *[!a-zA-Z0-9-.]*) exit 1 ;;
+        esac
+
+    ) ; then
+
+        # Looks like a remote file request; try to copy it into the temporary
+        # directory, bail out completely if we can't
+        dst=$td/$n
+        scp -q -- "$arg" "$dst" || exit
+        set -- "$@" "$dst"
+
+    else
+        # Just a plain old argument; stack it up
+        set -- "$@" "$arg"
+    fi
+
+    # Bump n
+    n=$((n+1))
+done
+
+# Run the command with the processed arguments
+exec "$@"
diff --git a/man/man1/swr.1df b/man/man1/swr.1df
new file mode 100644
index 00000000..8792b0ed
--- /dev/null
+++ b/man/man1/swr.1df
@@ -0,0 +1,37 @@
+.TH SWR 1df "January 2017" "Manual page for swr"
+.SH NAME
+.B swr
+\- run a command including remote file arguments for scp(1) retrieval
+.SH SYNOPSIS
+.B swr
+cat remote:.ssh/authorized_keys
+.br
+.B swr
+diff .shrc remote:.shrc
+.SH DESCRIPTION
+.B swr
+runs the command given in its arguments, first replacing any arguments in the
+form HOST:PATH with copies of the specified files as retrieved with scp(1),
+copied into a temporary directory that should be removed on exit under most
+circumstances.
+.P
+This even works for the first argument (i.e. the command), provided that it
+will run on the local system once copied in.
+.SH CAVEATS
+This only works for simple commands; you can't put shell syntax into any of the
+arguments.
+.P
+The whole script will stop if even one of its arguments can't be copied in, as
+there's no way to tell whether it's safe to proceed without some of the data.
+.P
+Don't even think about using this for mission-critical cases or situations
+requiring high security. It's a convenience wrapper.
+.P
+You may not need this at all if your shell has working command substitution and
+you find its syntax clearer:
+.P
+    diff .shrc <(ssh remote 'cat .shrc')
+.SH SEE ALSO
+scp(1), mktd(1df)
+.SH AUTHOR
+Tom Ryder <tom@sanctum.geek.nz>