Add Pager::skip_on_notty()

4 files changed, 52 insertions, 0 deletions

diff --git a/README.md b/README.md
index 03728ca..33b3766 100644
--- a/README.md
+++ b/README.md
@@ -59,6 +59,19 @@ fn main() {
 }
 ```
 
+Sometimes you may want to bypass pager if the output of you executable
+is not a `tty`. If this case you may use `.skip_on_notty()` to get the
+desirable effect.
+
+```rust
+extern crate pager;
+use pager::Pager;
+fn main() {
+    Pager::new().skip_on_notty().setup();
+    // The rest of your program goes here
+}
+```
+
 If you need to disable pager altogether set environment variable `NOPAGER`
 and Pager::setup() will skip initialization. The host application will continue
 as normal. Pager::is_on() will reflect the fact that no Pager is active.
diff --git a/src/lib.rs b/src/lib.rs
index 4e52caa..9dc80e8 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -49,6 +49,18 @@
 //! running as usual. `Pager` cleans after itself and doesn't leak resources in
 //! case of setup failure.
 //!
+//! Sometimes you may want to bypass pager if the output of you executable is not a `tty`.
+//! If this case you may use `.skip_on_notty()` to get the desirable effect.
+//!
+//! ```rust
+//! extern crate pager;
+//! use pager::Pager;
+//! fn main() {
+//!     Pager::new().skip_on_notty().setup();
+//!     // The rest of your program goes here
+//! }
+//! ```
+//!
 //! If you need to disable pager altogether set environment variable `NOPAGER` and `Pager::setup()`
 //! will skip initialization. The host application will continue as normal. `Pager::is_on()` will
 //! reflect the fact that no Pager is active.
@@ -67,6 +79,7 @@ pub struct Pager {
     pager: Option<OsString>,
     env: Option<String>,
     on: bool,
+    skip_on_notty: bool,
 }
 
 impl Pager {
@@ -83,6 +96,7 @@ impl Pager {
             pager: pager,
             env: String::from(env).into(),
             on: true,
+            skip_on_notty: false,
         }
     }
 
@@ -97,6 +111,15 @@ impl Pager {
             pager: OsString::from(pager).into(),
             env: None,
             on: true,
+            skip_on_notty: false,
+        }
+    }
+
+    /// Instructs `Pager` to bypass invoking pager if output is not a `tty`
+    pub fn skip_on_notty(self) -> Self {
+        Pager {
+            skip_on_notty: true,
+            ..self
         }
     }
 
@@ -108,6 +131,10 @@ impl Pager {
     /// Initiates Pager framework and sets up all the necessary environment for sending standard
     /// output to the activated pager.
     pub fn setup(&mut self) {
+        if self.skip_on_notty && !utils::isatty(libc::STDOUT_FILENO) {
+            self.on = false;
+            return;
+        }
         if let Some(ref pager) = self.pager {
             let (pager_stdin, main_stdout) = utils::pipe();
             let pid = utils::fork();
diff --git a/src/utils.rs b/src/utils.rs
index 084b48b..fb1f869 100644
--- a/src/utils.rs
+++ b/src/utils.rs
@@ -68,6 +68,11 @@ pub fn find_pager(env: &str) -> Option<OsString> {
     env::var_os(env).or_else(default_pager)
 }
 
+pub fn isatty(fd: i32) -> bool {
+    let isatty = unsafe { libc::isatty(fd) };
+    isatty != 0
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
diff --git a/tests/pager.rs b/tests/pager.rs
index d43909a..b9ca62f 100644
--- a/tests/pager.rs
+++ b/tests/pager.rs
@@ -12,3 +12,10 @@ fn nopager() {
     env::remove_var("NOPAGER");
     assert!(!pager.is_on());
 }
+
+#[test]
+fn notty() {
+    let mut pager = Pager::new().skip_on_notty();
+    pager.setup();
+    assert!(!pager.is_on());
+}