9_batch_processing.Rmd

title: Text manipulation
author: "Laurent Modolo"
output:
  rmdformats::downcute:
    self_contain: true
    use_bookdown: true
    default_style: "light"
    lightbox: true
    css: "./www/style_Rmd.css"

if (!require("fontawesome")) {
  install.packages("fontawesome")
}
if (!require("klippy")) {
  install.packages("remotes")
  remotes::install_github("rlesur/klippy")
}
library(fontawesome)
knitr::opts_chunk$set(echo = TRUE)
knitr::opts_chunk$set(comment = NA)
klippy::klippy(
  position = c('top', 'right'),
  color = "white",
  tooltip_message = 'Click to copy',
  tooltip_success = 'Copied !')

Batch processing

Objective: Learn basics of batch processing in GNU/Linux

In the previous section, we have seen how to handle streams and text. We can use this knowledge to generate list of command instead of text. This is called batch processing.

In everyday life, you may want to run command sequentiality without using pipes.

To run CMD1 and then run CMD2 you can use the ; operator

CMD1 ; CMD2

To run CMD1 and then run CMD2 if CMD1 didn’t throw an error, you can use the && operator which is safer than the ; operator.

CMD1 && CMD2

You can also use the || to manage errors and run CMD2 if CMD1 failed.

CMD1 || CMD2

Executing list of commands

The easiest option to execute list of command is to use xargs. xargs reads arguments from stdin and use them as argument for a command. In UNIX systems the command echo send string of character into stdout. We are going to use this command to learn more about xargs.

echo "hello world"

In general a string of character differs from a command when it’s placed between quotes.

The two following commands are equivalent, why ?

echo "file1 file2 file3" | xargs touch
touch file1 file2 file3

You can display the command executed by xargs with the switch -t.