Mirrors/rust-cookbook
2
0
Fork 0
mirror of https://github.com/rust-lang-nursery/rust-cookbook synced 2025-02-16 12:18:27 +00:00
Code Issues Projects Releases Packages Wiki Activity

Add "Process child process output continuously" example

Browse source 
fixes #339
This commit is contained in:
Ludwig PACIFICI 2017-11-27 22:35:08 +00:00 • committed by Michał Budzyński
parent b081b640cb
commit 8543f72ae1
2 changed files with 52 additions and 0 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

50
src/basics.md
View file

@ -12,6 +12,7 @@
| [Run an external command passing it stdin and check for an error code][ex-parse-subprocess-input] | [![regex-badge]][regex] | [![cat-os-badge]][cat-os] [![cat-text-processing-badge]][cat-text-processing] |
| [Run piped external commands][ex-run-piped-external-commands] | [![std-badge]][std] | [![cat-os-badge]][cat-os] |
| [Redirect both stdout and stderr of child process to the same file][ex-redirect-stdout-stderr-same-file] | [![std-badge]][std] | [![cat-os-badge]][cat-os] |
| [Continuously process child process' outputs][ex-continuous-process-output] | [![std-badge]][std] | [![cat-os-badge]][cat-os][![cat-text-processing-badge]][cat-text-processing] |
| [Filter a log file by matching multiple regular expressions][ex-regex-filter-log] | [![regex-badge]][regex] | [![cat-text-processing-badge]][cat-text-processing]
| [Declare lazily evaluated constant][ex-lazy-constant] | [![lazy_static-badge]][lazy_static] | [![cat-caching-badge]][cat-caching] [![cat-rust-patterns-badge]][cat-rust-patterns] |
| [Maintain global mutable state][ex-global-mut-state] | [![lazy_static-badge]][lazy_static] | [![cat-rust-patterns-badge]][cat-rust-patterns] |
@ -502,6 +503,55 @@ fn run() -> Result<()> {
# quick_main!(run);
```
[ex-continuous-process-output]: #ex-continuous-process-output
<a name="ex-continuous-process-output"></a>
## Continuously process child process' outputs
[![std-badge]][std] [![cat-os-badge]][cat-os]
Contrary to [Run an external command and process
stdout](#ex-parse-subprocess-output), while an external [`Command`] is
running, process its standard output without waiting it to finish. A
new pipe is created by [`Stdio::piped`] and it is read continuously by
a [`BufReader`].
The below recipe is equivalent to run the Unix shell command
`journalctl | grep usb`.
```rust,no_run
# #[macro_use]
# extern crate error_chain;
#
use std::process::{Command, Stdio};
use std::io::{BufRead, BufReader};
# error_chain! {
# foreign_links {
# Io(std::io::Error);
# }
# }
#
fn run() -> Result<()> {
let stdout = Command::new("journalctl")
.stdout(Stdio::piped())
.spawn()?
.stdout
.ok_or_else(|| "Could not capture standard output.")?;
let reader = BufReader::new(stdout);
reader
.lines()
.filter_map(|line| line.ok())
.filter(|line| line.find("usb").is_some())
.for_each(|line| println!("{}", line));
Ok(())
}
#
# quick_main!(run);
```
[ex-regex-filter-log]: #ex-regex-filter-log
<a name="ex-regex-filter-log"></a>
## Filter a log file by matching multiple regular expressions

2
src/intro.md
View file

@ -30,6 +30,7 @@ community. It needs and welcomes help. For details see
| [Run an external command passing it stdin and check for an error code][ex-parse-subprocess-input] | [![std-badge]][std] | [![cat-os-badge]][cat-os] |
| [Run piped external commands][ex-run-piped-external-commands] | [![std-badge]][std] | [![cat-os-badge]][cat-os] |
| [Redirect both stdout and stderr of child process to the same file][ex-redirect-stdout-stderr-same-file] | [![std-badge]][std] | [![cat-os-badge]][cat-os] |
| [Continuously process child process' outputs][ex-continuous-process-output] | [![std-badge]][std] | [![cat-os-badge]][cat-os][![cat-text-processing-badge]][cat-text-processing] |
| [Filter a log file by matching multiple regular expressions][ex-regex-filter-log] | [![regex-badge]][regex] | [![cat-text-processing-badge]][cat-text-processing]
| [Declare lazily evaluated constant][ex-lazy-constant] | [![lazy_static-badge]][lazy_static] | [![cat-caching-badge]][cat-caching] [![cat-rust-patterns-badge]][cat-rust-patterns] |
| [Maintain global mutable state][ex-global-mut-state] | [![lazy_static-badge]][lazy_static] | [![cat-rust-patterns-badge]][cat-rust-patterns] |
@ -164,6 +165,7 @@ community. It needs and welcomes help. For details see
[ex-check-broken-links]: net.html#ex-check-broken-links
[ex-check-cpu-cores]: basics.html#ex-check-cpu-cores
[ex-clap-basic]: app.html#ex-clap-basic
[ex-continuous-process-output]: basics.html#ex-continuous-process-output
[ex-convert-datetime-timestamp]: basics.html#ex-convert-datetime-timestamp
[ex-convert-datetime-timezone]: basics.html#ex-convert-datetime-timezone
[ex-crossbeam-spawn]: concurrency.html#ex-crossbeam-spawn