bash - Append or write to file using here-strings -


how can write file or append string file using ed only?

i have knowledge of other editors particular form of writing in bash script ed confuses me lot:

ed filename <<< $'a texttowriteinfile\nwq'

the previous line not work and, although have read ed man pages, still confused here-strings method. not interested in here-document method.

edit:

i've tried $ed h myfile <<< $'a\nmy line here\n.\nwq' h option , error 'h: no such file or directory'. have created file named myfile , sudo chmod a+wx myfile in directory.

tl;dr:

ed myfile <<< $'a\nmy line here\n.\nwq'

a sad truth programming can never automate don't know how manually. if don't know how append line manually ed, can't hope append line automatically through ed , here-string.

the first step therefore how append lines in ed. here's info ed:

the sample sessions below illustrate basic concepts of line editing 'ed'. begin creating file, 'sonnet', shakespeare. shell, input 'ed' must followed character. comments begin '#'.

 $ ed  # 'a' command appending text editor buffer.   no more grieved @ thou hast done.  roses have thorns, , filvers foutians mud.  clouds , eclipses stain both moon , sun,  , loathsome canker lives in sweetest bud.  .  # entering single period on line returns 'ed' command mode.  # write buffer file 'sonnet' , quit:  w sonnet  183  # 'ed' reports number of characters written.  q

ok, let's adapt append single line file , quit:

$ touch myfile $ ed myfile text here . wq

and let's verify worked:

$ cat myfile text here

yay. we're able manually append line, have recreate same input here-string. can use cat verify our input correct:

$ cat <<< $'a\nmy line here\n.\nwq' line here . wq

yup, input used. can plug ed: 

$ echo "existing contents" > myfile $ ed myfile <<< $'a\nmy line here\n.\nwq' 18 31 $ cat myfile existing contents line here

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