Working with vi editor through script

Question

I am working with a Korn shell. There is a log file which is continuously updating. I need to update this file and insert one character in it. I am writing a shell script for it. Can anyone suggest me how I can do it through script? I need to open and close that file using vi editor through script. Please suggest a way for it.

Here are the commands I use when I edit that file: vi my_file Press ‘E/e’ (to start edit) Press ‘i’ (to insert) Press ‘F’ (to insert missing F) Press: Esc -> : -> wq! -> [Enter] -> y -> [Enter]*

I need to insert one F at the beginning of first line in this file. Please can anyone suggest me how I can do it through vi editor?. I cant use any other editor like 'sed' because that file is continously updating.

Answer 1

vi is a "visual" editor. It's intended to be used interactively, by a human looking at a terminal and entering commands; that's what "visual" means.

---

The script-driven equivalent to vi is ex. (Often, ex is actually provided by your vi package, or even the same executable).

If you can write something in vi's command mode that will do what you want, you can feed that as a script to ex.

---

An example, tested against Apple's BSD ex:

ex -c ':open filename-to-edit' -c '1s/^/F/' -c ':wq'

An example tested against the ex shipped with vim:

ex -s filename-to-edit <<'EOF'
1s/^/F/
:wq
EOF

Alternately, without using vi or ex at all:

tempfile=$(mktemp)
{ printf %s 'F'; cat filename-to-edit; } >"$tempfile"
mv "$tempfile" filename-to-edit || rm -f "$tempfile"

Answer 2

I think you want an answer as

vi my_file <@ >/dev/null 2>&1
iF<ESC>
:wq
@

With the escape sequence of ESC, what you can enter by typing CTRL-V ESC
The newline before :wq is not needed, but makes this rubbish a little bit easier to read.

I am afraid this solution will work most of the time, until some logging is gone. vi makes a working copy of the file, edits the working copy and writes back that copy. Changes during the edit will not be seen. You can check this by opening the same file with vi in two windows. Or even in one window:

vi testfile <@ >/dev/null 2>&1
iFirstline
Second Line<ESC>
:r !date
:w
:! echo This line will be gone >> testfile
:wq
@

Now check the testfile.